i have a 89 k5 blazer. 350,tbi,205,14bolt W/488 gears,etc.. my truck wants to #### to 2nd gear at any speed over 40. at any speed when i let off the throtle it will shift into 3rd but as soon as i give it  any throtle at all, even just enough to keep my speed at a constant,it goes right to 2nd. the tranny is a new rebuilt w/ a shift kit. it has b/m trickshift fluid, it also has no kickdown cable. the trans and case both came out of an 83' 1 ton dually 4x4.  it does have the vacuum line hooked up to a manifold port. ANY help would be greatly appreciated. I am aching to get back in the mud.  

INTERESTING PROBLEM SOUNDS LIKE THERE IS SOMETHING INTERNALLY WRONG WITH YOUR TRANNY--VALVE BODY OR SOMETHING BUT I REALLY DON'T KNOW.  GOT A WARRANTY ON YOUR REBUILD?

thanks for trying to help.  no such luck on the warr. it was rebuilt,then sat for over a year.  

Did it have a TV cable or kickdown linkage in the donor truck? It might be a linkage adjustment out of whack? I'm not really have that much experience with auto trannies, but that's why I like a manual tranny...  

Trash in your valve body or your modulator is out of adjustment.