TRANSMISSION? OR FUEL FILTER?

Your message is not exactly clear.

When you say "slipping" do you mean you can hear the engine rev up, but the speed declines?

And when you say, "WHEN I PUT IT IN PARK I ACCELARATE." What do you mean? I'm sure you don't mean that when the truck is rolling you put it in park.

Just on what you wrote, it sounds like something with the transmission, but there's not enough information.

Well when I say slipping I mean that the engines decreases speed but the rpm is still high, then theres is a loud pop kinda like a pop of air coming from the muffler, also when the truck warms up enough nothing happens anymore it runs just fine, when it is cold all this starts happening

Unfortunately, more information is still needed.

You say that the engine decreases speed and RPMs increase. Do you mean the auto's speed decreases? RPMs indicates the speed of the engine, and as you know, the speedomoter indicates the speed of the auto. So, unless there are problems with the RPM gauge (which is possible, but not likely) the engine is actually increasing in speed.

However, with the limited information it does sound like it could be an exhaust flow problem. You might start by inspecting the exhaust system. Is there rust visible, or holes? It can be on the inside, and not visible. Besides the muffler failing, it could also be the catalytic converter.

I have the same exact problem (99 tahoe with 224k) Runs like a dream except for the that problem. I scanned the computer and had p0420 and p0430 pop up (1st and 2nd lower bank cat deficiency)
anyway, I got all new o2 sensors; 2 new flowmaster cats; plugs; and fuel filter installed and still get the same problem. A clunk comes from the passenger firewall when I step on the gas as it doesn't want to move.

The tranny works great all the time except when I first get in the car whether it is warmed up or cold.

I was told that changing the fuel/pressure regulator may be the next step----i hate this game of replacing everything to figure out what the hell is wrong!

Can it be a conrol module of some sort, or would a code like that pop up first?

Unfortunately, a lot of times it's difficult to know what is exactly wrong. However, a good mechanic should be able to figure out what the problem is before replacing something.

It doesn't sound like the fuel pressure regulator, because of the noise against the fire wall.

If you haven't had a good mechanic look at it. I'd recommend spending the $50/$60. The computer codes only report the syptoms.