My 02 1500 4.3 does not seem to have enough umph to climb even a gentle grade at highway speeds with the a/c on, I'm thinking that becuase the gears in this truck are so tall,... If I put the trans in 3rd instead of D I could bring the tach, up to about 2700 rpm wich would seem to be a little closer to the ideal power range, Will that damage the auto trans in my truck???

 

Not at all.

Are you sure you don't have a plugged cat or some such thing?

Allan