Ok, so I have a 1991 chevy camaro z28 with the 350 5.7L engine. Recently it started shifting into second gear very differently. Before, it would shift at about 2000-2500 rpm, and now its shifting at 3000 sometimes even 4000 rpm. Also, after i hit about 20 mph and it still hasn't shifted into second it feels like I'm just revving the engine until it hits 3000 and shifts into third. I read somewhere that it could be the TV valve or cable or something like that, and that I should try pushing the gas pedal all the way (while the car is off) and that that might loosen up the cable or something. Well, I tried that and it worked. It would start doing it and I'd just turn off the car and push it down a few times and it was like the cable got unstuck or something and it went back to normal. Now it wont work. So now I don't know if I'm supposed to clean something, or maybe not, or if its probably just going to be my transmission. If it is the transmission, I heard that I could get my transmission rebuilt for 550 dollars with the core, but so far I can't find it for that cheap. Help find it or solve my problem please? 
Also wanted to add that if you know a different transmission I could drop into my car that is more durable and maybe even cheaper I would greatly appreciate it.
Also wanted to add that if you know a different transmission I could drop into my car that is more durable and maybe even cheaper I would greatly appreciate it.