I just finished plowing put the Tahoe in park and left it running. Got out and back in went to shift out of park and the...

Sounds like the starter motor may be the problem. If you did the timing chain replacement yourself check to see if you disturbed any wires. In starter motor cases it'a generally the solenoid that's bad. Repair requires the starter motor be replaced. There are times when the solenoid may be sticking, tapping it may free it up. Either way the starter motor would have to be replaced. Hope this helps replacement is not difficult.