1985 chevy van with th 350 really clunks when it shifts. Whenever I back out of the driveway it will shift through all of the gears smoothly. Next time I stop and go through the gears again in really clunks hard into each gear. I f I stop at the light and put it in reverse it will shift smoothly again 1 time through the gears, next time it clunks again unless I put it in reverse first. The only thing I can think of is the govenor is sticking and put ing the transmission in reverse frees it up.