Neil.96

Hi, I have a 2000 GMC 3500 that is a commercial production unit so it still has the body styling of the 88-98. We towed real heavy with it one day on the farm and now it only likes to move if my foot is to the firewall. It does it in reverse as well. I believe it is a 4L80e but have not climbed under to confirm as I do not know what I'm looking for. could this be bad shift solenoids? any other ideas?