Sierra hesitation/misfiring

I have a 2000 GMC Sierra 1500 6 cylinder that started hesitating when i try to go up hill or accellerate. It is now getting worse and misfiring. I could barely make it up the driveway. I changed the fuel filter and put fuel injector cleaner in my gas tank. What would you recommend I start looking at to solve the problem?

a tune up might help. distributor cap/rotor, spark plug replacement. does it have any codes?? it should if it's missing. get it scanned.

I took the truck to a mechanic and he hooked it up to a diagnostics and it is showing no codes. He ran a fuel pressure test and after that it seemed to run fine. Once I left the shop, it seemed like it was not getting any fuel. My truck stalled, I started it back up and it ran fine for a few miles then it started again. I also changed the spark plugs. Do you think I could have something in the gas that is causing the injectors to clog temporarily? When I restart the truck could the pressure from the fuel pump clear the injector? What do you suggest?

I would change the fuel filter again, its not unusual for them to come apart inside and block the line on and off.
I had this happen once, really a pain to sort out.

Do you think there could be water in the tank?

Its possible if you don't think you got it from a reputable gas station, but I would lean more towards something else, like a bad fuel pump or pump relay.
All of this is only as long as ignition stuff like AMAC209 said was taken care of first, look for ignition coil connections, module connections, etc, etc.

It turns out it was the fuel pump, distributer cap, and rotor. This truck is a 2000 it seems like that stuff shouldn't have gone bad that quick. We have a 1999 Ford Taurus that has needed nothing except oil change etc.. Oh well at least it's fixed and running great.

It turns out it was the fuel pump, distributer cap, and rotor. This truck is a 2000 it seems like that stuff shouldn't have gone bad that quick. We have a 1999 Ford Taurus that has needed nothing except oil change etc.. Oh well at least it's fixed and running great.

Look at your distributor at the pick-up at the bottom of the distributor and see if the magnet is busted or cracked. May have to replace the whole distributor costs about $100 to change it out.

Bubbabryan, I think its more than that for a 2000 V6 distributor. Erethage, is there an air conditioning line above the distributor? If there is add some more insulation to it. There is a TSB out on 4.3L v6's and condensation dripping off AC line causing them to arc out