Stop and go stumble

I've been trying to find the root to a bad stumble when accelarating from a stop. I want to say that it started after I did the Z/28 cluster mod but unsure cause it started getting hot outside shortly after I did this. The pressure sending unit was changed as well as the resistor, but I did notice that if the weather was at 100* or better and the wagon was either at or close to 210*, then the oil pressure would start to drop and start cutting the power to the fuel pump. So the pressure unit was changed for a new one and the stumble is still a bit noticible but not as bad as it was. I also noticed that the valve that sits under the battery along with the vapor canister, vibrates and makes a buzzing noise when the weather is hot ? I pushed on the inner fender well the first time I heard it making the noise and could feel it vibrating ? All three componantes were replaced last year about this same time last year, the canister, the valve and the relay; along with all the rubber hoses that connect them together. The last thing to mention is the underhood temp, I realize it's the engine temp plus the nice weather here in Lost Wages but it just seems a bit more than I remember. This may seem a bit stupid but does the air deflector under the front bumper make that much of a difference ? Mine was rather damaged and removed but I was planning on ordering a new one.