Have a new one piece driveshaft made... if possible. Rule of thumb the driveshaft can be one piece and have the slip joint in front if it is less than 5 feet. You might need to make the driveshaft out of 4 inch tube. Any competant driveline shop should be able to make you a new driveline for less than $500.

A t5 might be a bit light for a working 3/4 ton truck... espeacially a 5500 lb. panel truck. You might consider a stronger transmission if you plan to use the truck.