Strange problem

I have a 94 Sierra K1500 with a 350 and an auto trans. This truck runs great every where except if I am going over a steep incline. We have a very tall bridge that has a moderately steep incline on a highway so the speed limit is 70 mph. If I have the cruise control on it will start to hesitate and stumble and will eventually down shift and run up to 3,000 rpm to maintain speed. If I don't use cruise it will still hesitate and stumble and I will have to almost put it to the floor to get over the incline. There are days however that it will act completely fine and stay at 2,000 rpm and you would never even know you are going up hill. I have replaced quite a few parts and I will include a list. I have taken it to the dealer and they could not find anything wrong with it. I am not sure if this is related or not but I am also getting about 10mpg and there was a couple of occasions where I was missing upwards of 3 quarts of oil.

I have replaced the fuel pressure regulator and spring, coolant temp sensor, oxygen sensor, vac lines, throttle position sensor, egr valve, cap, rotor, plugs, wires, coil, map sensor, and the exhaust system from the manifolds back.

Any help would be appreciated. I have about given up hope.

I had that problem in a 96 ford and it was a low volt reading from the mass air sensor.

Thanks unfortunately I don't have a mass air flow sensor. I will add a little more information also. I have recently replaced the fuel filter and this used to be a problem that started out as an every now and then thing and now it is every single day..I guess there was one day last week where it acted fine. I thought this may have been a temperature or weather related issue but in the past few days here in Michigan it has been warm rainy and snowy that covers all 3 seasons we get here.

I would check fuel pressure, if TB it is 10-15 psi.

Thanks I am going to try and make it until Christmas when I actually have some time off of work and then take it in and get the fuel pressure checked.

I had the fuel pressure checked and it is fine. I also did some additional testing and found that if I go over the same hill in 3rd gear I do not get any hesitation or stumbling.

By not pushing the truck in overdrive you are taking the load off the engine, it is possible you have some wires and plugs misfiring, this would only happen on a slight incline in o/d just before downshift. On rare occasions a bad o2 sensor could cause this also.

Last night I changed the plugs and wires and on my way to work this morning it seemed to run a lot better. We will see on the way home if it is still behaving.

Its been a while since I have written but 2 days after I replaced the plugs and wires the problem came back and now it seems a little worse. Now its hesitating when Im just trying to get up to speed. I have a new theory of maybe a head gasket blown between cylinders????

I am far from expert in diagnosis, but I can tell you that I had a quite similar problem with a 350 that I had in a Chevy, and the problem was water in the fuel.

After tearing my hair out over this problem, I finally discovered that mice had chewed a hole in a rubber hose connection in the line that returns fuel vapor to the tank. The result was that the hose was sucking in moisture from road spray, since the section with the hole in it was down low.

A very inexpensive check of this possibility would be to chuck a couple of bottles of isopropyl alcohol into your fuel tank and see if the situation improves.

Your oil consumption problem may be unrelated to the power problem.

A head gasket bad as you describe would show a loss of coolant also that type failure is rare. Sluggish is one thing a misfire ia another, usually in a tbi engine misfires are strictly related to ignition problems, sluggish can be more complicated, maybe a full scan is in order here.