1987 GMC S15 problems going up a hill

My 87 gmc s15 runs great the only problem is when im going up a hill it will rev up like its sapost to then it will rev down all the way then 2 seconds later it will rev up again. Then when im going down the road it will do that again, and i have to give

Ive changed the air filter ran a few new vacuum lines, changed the fuel filter, regular tune ups, and ran lucas engine cleaner through it.