Just got my Pete 387 back from the shop. Had an Eaton FullerFRLO16410C TRANSMISSION put in last week. The truck started right up and drove the 80 miles home with no issues. Went to start this morning and get nothing. Not even a click. Batteries tested ok. Tried pull starting thinking maybe the starter. Wouldn't crank. Now thinking the problem may be related to the new tranny being put in. This truck/tranny won't start if in gear even with clutch down. Get the same nothing I'm experiencing now. Could the computer think the truck is in gear? Have no idea what to check. Appreciate any input.

There should be a starter relay switch in the circuit, it's normally found in or near the battery box on most trucks. Check for 12 volts at one of the small terminals, when the key is turned to start. If juice gets there from the key switch, try tapping on it to see if it's stuck.