350 stutters/shakes on upshift

[Domer]

I have a 77 C10 2wd, dont know if the trans is from that truck or not. it is a TH350, when im driving just normal and it goes to upshift to 3rd, it feels like a stutter/shake then it will shift, sometimes i have to back peddle to get it to shift. anything in particular to look for when i pull the trans? Im going to do a rebuild, just wanted to see if there is something i should look for, unless a rebuild isnt warrented and its something simple??
Thanks

 

[plantman]

check the modulator for vacuum leaks. check vacuum lines to the modulator. check for vacuum leaks on the #8 intake connection. Make a note of the level and color of the trans fluid--sb red and clear

 

[89Suburban]

 

[Domer]

I ended up taking it to a shop, and it was just wore out. needs new seals and bushings. but nothing broken. so $600 later i will have a good working th350 again..