does the truck have the check engine light on, first step, fluid level and condition smell the fluid, if the light is on get it scanned ( you could purchase a cheap scanner from ct but some do not scan the tcm ) hopefully like you say its just a shift solenoid, as this would be your cheapest option. How many km's on truck? if you want pm me, and I will try to point you in the right direction, right now the industry is slow so there will be lots of factory trained techs looking for a side job
good luck