97 Bravada starting issues

I've had issues with starting my truck when it sits for 12+ hours and the longer it sits the harder it is to start. I have been surfing this and the blazer forums looking for a solution and it seems like a common problem.....but no one ever posts if they solved the problem and what fixed it. I put in all new plugs and wire <AC delco plats...even that drivers side middle pain in the ass one> fuel pressure test turned out good, starter and battery are solid, replaced the vacume lines going from the ball on the hood to the PCV and put in a new PCV. It throws me an Emissions/EVAP code intermittenly <usually on the rougher starts when it has been parked for over a day>. If i just jump in and start cranking it won't even give a hint of wanting to fire. If i cycle the fuel pump < 3 times when it sits over night, 6+ if it sits longer> she coughs a bit like its misfiring but then starts up. Runs great after that and fires right up if has been sitting for 8 hours or less, good gas mileage. The rpm's bobble slightly when it is in drive and stopped at a light but not at all bad. I have noticed a hissing coming from the top of the gas tank when it is running <not a humming like the fuel pump running>. Took off the gas cap and got a big woosh with it running, shut the engine off after a couple of minutes and immediatly took the cap off and there was no woosh at all. Cycling the pump and instant loss of tank pressure when vehicle is off tells me it has to be a pressure issue but 63 psi that bleeds down to 55 over 10 minutes tells me its not. Sorry for the lengthy post but I wanted to give all the info I have. Any help is much appreciated.

After researching this for over 8 hours I am leaning towards the fuel tank pressure sensor that is mounted on top of the fuel tank.....$38 part and I am almost out of gas so perfect time to drop the tank, check the harness, replace the vacume lines, and in my book it says to change the charcoal filter in the emissions canistor....Won't get to this for a few days but I will let you know how the fix goes.

You have 62-65psi fuel pressure at the Schrader valve?

http://i131.photobucket.com/albums/p288/Clunk_/Image026.jpg

Tested pressure again after it sat over night before priming the pump and pressure was low. Still hearing the hissing from the top of the tank when it is running. I let the fuel level get low since I planned on dropping it this weekend. When I shut the engine off I could hear a clunk from the rear end after it got below 1/4 tank. The clunk is the gas tank flexing from instant tank pressure drop. So the tank is sucking in the sides and not venting while running. From reading on here and the blazer forums I learned that this will throw the emission code I have and the computer adjusts the air/fuel ratio causing the rough idle issue. Instant drop in pressure and hissing sound tells me this caused a leak over time. What should I check besides vent valve, vacume lines, and the seal around the fuel pump locking ring?

I have a problem with your gas cap. I haven't had one "whoosh" air in or out since the 70's with sealed systems on cars fresh off the freeway to the gas station where I worked as a pump jockey.
What do you think of the possibility a faulty gas cap?

Could be the gas cap i suppose, the rubber gasket on the one I have does show signs of wear. The gas tank hissing and not venting when it is running but instant loss of pressure when truck is turned off makes me think it is more then a gas cap though. May as well pick up a new one when I go pick up the vacumme lines and what ever else looks deteriorated.

There are several EVAP DTC's, which one is being set? Don't start replacing parts needlessly, we can help you diagnose it correctly.

Sorry for such a long interval since my last post. I have been busy fixing the little things on the truck in my free time. So here is my update. The only trouble code the truck has thrown since i bought it was the evap emission code, that was solved by replacing the swiss cheese vacume lines under the hood. Truck started overheating on me a couple weeks ago, guessing that was due to air pockets in the system from when i flushed the engine~ ran heater and AC for about 30 min each and kept topping off the coolant~ problem fixed. Threw a new gas cap on her just to be sure since it was cheap and never hurts to replace the caps every so often. My cold start issue is still unresolved but I have found a trick to living with it for now~ turn key just enough to engage the starter for a split second, 3rd time around she pops right off, kinda seems like she wants to flood just a little bit before fireing up. Fuel pressure is in the specs listed all over these forums until I get to about 1/4 tank of fuel then pressure drops considerablly and the tank flexing starts when i kill the engine, while running the pressure is good. Also below a 1/4 tank she will die on me if I am stopped on a downward incline. Again not really worried I can just keep the tank full for now until i get enough free time to rip into her. I noticed just a few days ago that my break pedal was getting a little soft. Driverside front break line at the caliper was only finger tight and the bleeder screw wasnt tightened properly.....started to bleed the brakes and eventually get a solid pedal, at least until I fired the engine up then she went to the floor again. Decided to try bleeding with the engine running. Every time I would pump the breaks the rpm would drop and almost stall the engine and then rev itself up to around 2500 rpm for a few seconds, normal idle is 800-900. This confused the hell out of me but i got the pedal solid so didnt worry about it....until now because since doing that my rear window are stuck in the down position. Since it is highly unlikly that both motors would go out at exactly the same time and right after the hinkey break pedal rpm issue, I am thinking all my problems are electrical issues? Electrical and wiring is my downfall when it comes to vehicles, no clue where to start looking or even what to look for. Any hints or tips would be much appreciated....brand new interstate battery that was load tested upon purchase btw. Thanks guys

Glad you found and took care of your brake issue.

The rear window issue could be a bad fuse and if your fuses are ok then there may be a ground issue. Since most switch connections are made on the ground side on the Bravada, among other vehicles, a poor ground will keep electricals from working even if there's positive power at the part.
I'll do some checking.

Check the Rear Window Lockout Switch near the driver. Should be something in the Owner's Manual to describe this.
It's there to keep the young'uns from playing with the rear windows while you're trying to drive.