how do i stop transmission slipping

If it were me, and I know you probably already checked trans fluid level, ,,, try adding some lucas oil trans stop slip additive, ,,works,,,,,,change filter and fluid, suggest pulling pan so you can see what kind of wear , clean very very good, no silicone on gasket when reinstalling, careful not to double up o ring on filter. I hope this helps and its not already everything you have done. 96vaner

Change the transmission fluid and filter, add Lucas transmission fix and hope for the best as you probably need a re-build. Don't over fill the fluid!

here is my experience... I have a 97 silverado with a 4L60E transmission, automatic. I inherited it and there was no documentation that the transmission was ever serviced..I did a motor swap after the motor blew from an catastrophic overhear (don't ask! lol)...anyway, at the time of the swap, my mechanic CAUTIONED me about the consequences of doing any transmisssion servicing. He urged me to take this advice seriously. Well, he was right! I went ahead and did a trans fluid flush and a filter change and within 200 miles the transmission failed miserably. no 3/4 and slips in reverse...never can get past 2nd gear. Apparently, what happens is when you have a high mileage 4L60E that was never serviced, the transmission fluid contains particulates/contamination and a "heavier" viscosity that is actually holding the cluck pack together..you put new fluid in, you basically lose all that "old friction" fluid, and you take the chance of pushing old debris from spaces that collected into passages, across plates, into seals, etc..and you get rapid failure. So what I am saying is, if you are going to do a transmission service, a flush, or even a filter replace, or all of the above, then be prepared to see failure...especially if the transmission fluid and filter have not seen service ....And a new or remanufactured transmission is miserably expensive. I should have listened to the advice of my mechanic at the time of the motor swap..due to unforseen financial difficulties this same truck has been sitting in my garage for almost a year now, and I am now only finally able to get a good reman 4L60E...it was an expensive mistake doing the service in the transmission...so, just be prepared...If I could give advice on what to do, is to do nothing on the transmission at all, unless you are 100 percent confident about it, or you have the cash to have it replaced. the thing you can do, to help you determine that is by sampling the condition of the transmission fluid....if it is really dark, smells burnt, and has the "gray matter"...leave it alone and let it fail on its own timeline. this advice is counter-intuitive..most people will automatically assume these are bonafide reasons to get a fluid and filter change done asap. this is not actually wise, unless you are prepared to deal with a quick and fast failure after that change. The same advise does with the "magic in a bottle" solutions you read so often, like Lucas fix...same thing can happen..you end up changing the properties of the fluid sufficiently that those deposits and "friction matter" circulates to areas of the transmissions in ways, that actually destroy it rapidly.... the other lesson, obviously, it to pay special baby care with doing regular transmission services...even perhaps going synthetic early on, installing a trans temp and pressure sensor, and a better more efficient trans cooler to help preserve your trans..and be careful how you tow heavy ...mountains...hot weather...etc.... when my new reman goes in, it's only amsoil syn fluid, and all the upgrades mentioned above...a small amount of preventative maintenance and some better ways to actually monitor trans performance should allow the transmission to last a very long long time..that's my story..I'm sticking with it.

I have a 1999 Chevy Cheyenne single cab long wheel base it will on drive in 1st and 2nd gear? How should I go about fixing the problem or finding out the problem.

I've got a 94 chevy z71 it's got a350 in it I put a auto zone trans in it .when I pull a trailer it blows trans fluid out the front seal .and its weak.if I just drive it around not pulling anything it never leaks fluid .I've put in 3 front main seals.im no stranger to working on vehicles. But this has me stumped any ideas .it isn't slipping either.