When i step on it (kinda) fast theres a rattling sound on the trans, but when i step on it slow the gears go in smooth and without a problem???

 

are you sure its the trans, could it be lifters maybe doing it? what engine and trans? so when it does it is the car jerking or losing power.

 

5.7 engine-trans 4L60 and when i revv it the RPM's just go up and the car wont advance but if i step on it slow , now thats when it will take off and the gears will go in nice and smooth...

 

sure sounds like belts are going inside the trans. did you check fluid level

 

do you use 93 octane gas ,they demand it ,if trans could need a flush ann new fluids

 

cruising on down the road and put the gas down and the rpms rise but it goes nowhere is called....................slipping

if you continue to drive it that way, the transmission will overheat, the fluid will burn and the rebuild will cost more than what the rebuild that you need will cost if you stop driving, yanking the trans and getting it rebuilt

As an aside, with the trans out, it's a great time to repalce the rear main seal in the engine. It's right there and you may as well use the opportunity.

Oh, and if you are yanking it yourself, do strap the trans to the trans jack. When transmission meets head, the head loses. I took on a 700R4 in my '89 and lost. I then made sure to strap the trans each time I removed it from my 95Z for the 3 rebuilds (yes 3 rebuilds) that I had done (it happens when you make too much power)

If you can remove/replace yourself, and have an alternate vehicle you can use, find a cruise night or car club and ask around for opinions as to who does an "honest" bench rebuild. If you're stock engine, you don't always need new hard parts but it never hurts to upgrade servo and the sunshell

here's a generic version of "the beast"

Transmission Drive Sun Shell Heavy Duty Monster Beast Extreme Strength Washer Ty | eBay

here's an upgraded servo but shop around

New Complete Corvette Billet Second Third Fourth 700R4 4L60 4L60E 4L65E Servo | eBay