I have a 94 4.3L V6 C1500 Silverado and im having issues with it shifting into 2nd 3rd and 4th gears... when the problems first started my truck kept stalling out as soon as i would start it and when ever i would get it started the engine would cut out when shifting gears...i have relplaced several things: throttle body seal, E.G.R. valve, new spark plugs and wires, distributor cab and rotor, fuel filter, i had a busted engine mount so i had that replaced and it no longer rocks, the thermostat has been replaced, the fuel pressure has been tested and its right where it should be, i put a new air filter in it also.... all this has helped the stalling for the most part except for occationally when i put it in reverse but it still cuts out during shifts in the 2nd and 3rd gears and it has trouble shifting into 4th, it kinda sits in thrid until the rpms get real high and then shifts into 4th... it has tripped a code that says its running to lean but i was told its probably because i have a high flow exhaust and that it shouldnt hurt anything... im kinda confused on what else i can do or what else may need to be replaced if anyone can help itd really be great!