tranny or cat. converter? - hey guys i have a 94 gmc sierra 1500 4wd Pu 5.7 liter AT. the problem im having is at low rpm it feels like ...

hey guys i have a 94 gmc sierra 1500 4wd Pu 5.7 liter AT. the problem im having is at low rpm it feels like its surging slightly, going up over a pass its shifting down more often then it should. it also is now getting extreamly bad gas mileage. i replaced cap, rotor,plugs and wires. the tranny does not slip and shifts fine, the transfer case works fine also. no whinning sound. all gears seem to work fine in trans auto or when i manualy shift it. no code is shown.i havent changed the fuel filter in the frame yet. could it be the cataletic converter ? i put my hand over the exaust pipe and it does not feel like theres very much pressure coming out. i seem to get more pressure out of my geo exaust than my trk. it feels like its being restricted going down highway like im got some power loss. any ideas or help would be much appreciated. i dont want to buy a ct. converter if thats not my problem

thanks

Sounds like a bad catalytic converter is possible. Remove the O2 sensor from the exhaust pipe and take it for a ride. If driveability improves - the cat is plugged.

ok ill check that thank you

that didnt work made it run worse,start to give it gas and starts sputtering at low rpm. someone mentioned a tps or iac valve

Had a fuel pump develop low pressure on truck. Ran great at low speeds, replaced pump and everything was fine. Never had that happen again. Would check fuel pressure.

i have a 94 GMC cierra P/U 4X4 C1500 SLE, 5.7L, TBFI, A/T. approx 150,000 Miles.
im getting a slight surging when traveling down the highway, transmission down-shifting more than normal,bad gas milage,feels like im driving against a head wind.runs fine at a idle. when in gear, stopped on a hill, when barely throttling the engine up (just before the truck starts to move) it starts sputtering bad then smooths out, keeps doing it over and over. in netual i stomp the throttle down and it will sometimes pop. i have replaced: Cap,Rotor,Plugs,Wires,Caytiletic Converter and O2 Censor. which all but 02 censor needed replacing. i have no check engine code showing anything. hve checked throttle position censor it checks good. still havent tried my fuel pump yet,i did replace it about 10,000miles any ideas????????? thank you

I had the same thing happen with my 2003 seirra. At about 123000 miles, it would downshift when going up hills on the highway. Yesterday, I was traveling up a hill and the rpm's jumped to 6000. I pulled over and found that I could still move forward. When my truck shifted into 3rd gear, it reved up again. Took it to the loal dealer who informed me that I have blown 3rd gear and up. Needs a total rebuild...hope this isnt the issue that you are developing.

no. i have a A/T and it shifts fine,just downshifts more mthan normal due to lack of power or something holding me back