4l60e automatic transmission problems

[Troy heath]

Hey I have a 1999 Chevy Silverado 1500 extended cab z71 4x4. With a 5.3l vortec motor 4l60e automatic transmission. I bought it recently an the previous owner said the motor an tranny we're freshly rebuilt. But told me the shift solenoids needed to be changed.  For the price an having a little project to do I bought it anyways. I'm no mechanic but willing to learn anything. When I put it in drive sometimes it shifts smooth an occasionally it slams into 2nd gear an revs out won't shift to 3rd. When i manually shift into 1st, an 2nd it's shifts smooth, when I switch to 3rd it to revs out. I have reverse too. plugged machine to it an 2 codes popped up po449 and po506. No transmission code though. ive had enough bad luck so im praying this is a good sign. I've heard speed sensor an possibly shift solenoids. My question is, What's your suggestion to what may be my problem? Thank you for your help in advanced. 

[davester]

Are you sure the machine you hooked it up to could read codes from the TCM (transmission computer)?  The basic ones don't.

[Troy heath]

Possibly was the basic one. Any ideas on the the problem With my description?

[davester]

no idea.  i would suggest finding someone with/buying a code reader that can at least read tcm codes to perhaps give you some idea on where to start.