SSJ

Ok, so heres the problem. I just bought a 2000 Silverado reg cab,2wd, stepside with a 4.8, auto trans and 373 rearend. 103k. I drove the truck a couple of times before purchase and it had already been warmed up by the seller prior to my driving it. The first morning after the purchase I started it up and I could hear a low growling from what sounded like the transmission, to me. It went away after a few minutes of warmup. When it shifts from 1st to 2nd it shifts hard like it would if it had a shift kit in it. The other shifts from 2 to 3 and 3 to 4 are normal and smooth. I asked the seller a few days later if there were any transmission problems. He told me that the noise I was hearing was the power steering pump and it has done that for 6 months or so and it had always shifted that way. No problem, minor fix I thought and was to be expected with a used vehicle. I replaced the pump today and thought all was well again until I finished work and the growling was back at startup. Turns out it isn't the pump afterall. The growl is still there until the truck warms up and then it goes away again until it sits and cools down for a few hours. Is this growl and hard upshift something that is normal for this drivetrain? Anyone else had similar problems and how did you go about fixing it?

SSJ

Well, I,ve solved my problem with the growling that I thought was coming from the transmission. Turns out it was only an idler pulley that was going bad and the bearing was causing the growl until it warmed up. The hard upshift between 1st and 2nd hasn't been resolved yet. I haven't checked on that aspect of the repair yet but from what I've been reading in other posts it may only be as simple as replacing a shift modulator on the transmission I'll update with the results again as soon as I can get the repair done.

BlackOnBlue89gmc

Just for good measure check the fluid level I had a Cherokee that I put a junk yard tranny in and I filled to right below the line and it would shift hard until warm up so I added a half quart until a hair past the line and have had smooth shifts since