I have a 1976 Ford F100 with the 300 inline 6 engine, four on the floor. I am having an issue shifting gears, only after I have been driving/shifting for approx 15-20 mins. This happens both on the highway and in the city. The only thing that is missing from the engine bay is the fan shroud. Could it be overheating something, thus making it harder to shift gears? This is my first older vehicle I own. I bought the truck as a project, to flip, then fell in love with it. Now I can't let it go. My daughter and I love this truck. Any help is greatly appreciated in advance.

 

Since no one else has chimed in I will take a stab at this even though I'm no expert... On my 78 f150 with a B/W T-18 I changed the fluid soon after I bought the truck. I used 80W90 in my transmission but I do not drive it in the winter. I have heard that Ford wanted you to use 50W motor oil in a T-18 if that is what you have. Does your transmission have a granny gear first? If so Ford recommended that you start out in second most of the time unless conditions warrant a first gear start and that gear isn't a synchronized gear so you can't shift down from second to first in that case while on the go. Also, if your synchros are worn, downshifts are easier with a little throttle before going into the lower gear. Do you do that? It might tell you something. When I first changed my fluid half was water and half was gear lube. It can't hurt to change it out but the new fluid won't automatically mean better shifts as it's not broken down like your old fluid. There's also the clutch free play you should check that can change after everything gets warmed up...Maybe the real pros will say more, good luck!