Diesel Bombers - a518 trans please help!

i have a 93 d350 2wd auto that i have just finished building...... this truck sat for about 5 years and was only used as a farm truck. i have had it on the road for 2 weeks and it has never once in that time shifted into overdrive!..... before anyone asks, the first thing i did was throw away the TPS and installed a potentiometer. still no overdrive! it worked when we used to drive it! why did it just give up!...... i have grounded all of the stupid temp switches and have grounded the overdrive solenoid witch i was told i was supposed to hear kick in (i heard nothing).... i left it grounded and have been driving it.... still without overdrive. i have a FSM (a real FSM) but the trouble shooting sections are vague and i have no idea how to test my overdrive switch properly..... it does get power though! i know that! i just dont know what to do!...... i am about to install a new overdrive solenoid tomorrow and a shift kit while im at it....... i have no idea where to go from there if it doesn't work. i crawled under it today and plugged in my new overdrive solenoid and nothing happened so im not sure what to think about that, but then again i dont know much about automatic transmissions to begin with.

please anybody...... i have no idea what to do with this stupid transmission:argh:.