HELP! 02 SILVERADO TRANSMISSION PROBLEM?

[thokemechanic]

Hello!

I was wondering if anybody could help me out, as I am stumped. I have a 2002 Chevy Silverado 1500 4x4 5.3. I had the transmission rebuilt about 35,000 miles ago because it went out. The problem I am having now is that it does not want to shift out of 1st gear unless I release the gas, and the other gears shift on their own. When it does shift, it is not hard at all. If I romp on the gas pedal (put it to the floor or 3/4 way) it wants to rev up high in RPM's but does not want to go anywhere. If I press on the gas pedal anywhere to 3/4 of the way it goes high RPM's and then will shift. It is strange that it does not shift hard when it ends up shifting through the rest of the gears. I replaced the solenoids on the valve body and it did not fix anything. I checked the transmission fluid and it was a redish brown color with metal flakes in it (fluid has not been looked at since rebuild). I put new fluid in it, but it is still doing the same thing. The only codes that are popping up ate the P420 code (which I know is my cats). Otherwise, it runs great, just the weird possible transmission problem. 


Any suggestions of what this could be?

[garagerog]

Clear up your cat issue before delving any more into the transmission, check out #1 in the following link:  www.buehlerauto.com/Articles/Article-Component-Failures-Disguised-as-Trans-Pro

[thokemechanic]

I can clear the P0420 codes with my computer and they stay off for about a week. When the codes are off it still acts the same way. It wasn't doing this, and just started to do this about 2,000 miles ago. I was told by a transmission shop that the cat's wouldn't cause the weird transmission problem. It is like it is slipping almost when romping on the gas pedal. Just high RPMS and then it will shift. It is only 1st gear that won't shift on its own. Do you believe the cat's are still to blame?