Not shifting into 4th gear, even after reaching operating temp.

I changed the valve cover gasket yesterday, and after doing that the van ('95 2wd DX AT) won't shift into 4th. It acts like it does when the engine is cold. Is the temp sensor wire close to where the valve cover is and i possibly bumped it?

Any thoughts?

There are coolant temp sensors near the valve cover. They are in the coolant neck (Toyota calls t "water outlet") that comes off the top of the head over cylinder #1 then bends down, leading to the hose that goes to the radiator.
You can see the green and black senders pretty clearly in this pic (not mine):
http://i.imgur.com/HtrzYZT.jpg

The green coolant temp sensor in the head was unplugged.... it was an easy fix to plug it back in and the van is still running perfectly.

Thanks,

Merdlb