f150 won't come out of 4wd?

[RG5384]

Bought a truck for the lot, payed someone to drive it back, drove it all the way back in 4wd low(about 30 minutes at 60mph...i know, i know....). The truck will not disengange out of 4wd, it transfers fine from 4wd low to high, but will not go into 2wd mode. It is the work version of the f150 and thusly has the manual selector, automatic trans. I do not know if the problem was there before it got driven in 4 low on pavement at high speed for a long time or not, so that may or may not be a contributor. Any ideas? Mechanic says the shift linkage is fine. Thanks,
Ryan