i own a 92 model with the lt1 and a automatic trans. my motor has developed a strange problem that neither me nor my mechanic can figure out. the vehicle has, and i'm not lying about this, 267,700 miles on it. my problem is that the motor stumbles very badly until it hits just above 3000rpm, then it pulls like there is no tomorrow. now heres the list of parts that have been changed on the car. the timing chain, fuel sending unit, fuel pump, filter and injectors have all been replaced as well as the optispark unit ( twice ). i'm running a 160 degree thermo on the car as well as a msd 6a spark box. the thermo is still in the car because of the fact i had a chip in the car but took it out due to the serious drop in fuel mileage that resulted after i initally installed it. hypertech could never explain why that happened and they reburned the chip several times for me but to no avail. the best way to explain what the motor is doing, is that its acting like it has a turbo on it and your waiting for the turbo to wind up ( meaning just like turbo lag ). one thing i am wondering about is could the msd box be doing something not quite right and is causing the problem? any help you guys can give would be greatly appreciated.

thanks again,
allen  

What sounds like is happening, the motor doesn't have enough timing until it hits 3000 RPM, then it has a ton of advance kicking in and starts to run properly. I'd look at your MSD box as the possible culprit. It could also be the opti-spark is going south again. Those unit are notorious for problems. Maybe try the new MSD opti-spark replacement?

On your thermostat, that could actually be hurting your performance. F.I. equipped, computer controlled motors are very sensitive to thermostat changes that use a lower temp than stock. Whiel someitmes you will get more horsepower, usually you just end up with bad gas mileage and lower horsepower.