I have an 86 K10 that overheated yesterday... Reason being my transmission won't shift after 35mph (into third or whatever it would be). This being said I know fluid level is good I recently replaced and have the TV cable set up and was working fine the past couple months but all of a sudden it's like it slips out of gear. After it slips out rpms just go up as you rev the engine but it won't go anywhere until slowing down enough for it to downshift back into gear an then the process repeats trying to go over 35?