96 International 4700 Rollback Dt466- have some ??? about trans and motor.

Hi, I recently bought a 1996 International 4700 with a dt466 mechanical rollback tow truck. It has been sitting for about 6months cause i'm doing body work on it. now it is time to get on the road. The two major problems I'm having has to do with the trans, which is a 6 spd manual with a low gear. I drove it today and it seems to be shifting into to all gears ok, but i'm have some trouble down shifting. Is there anyone out there that can make any suggestions on what could fix this issue besides, having to drop the trans. Also The dt466 starts right up and runs pretty well, except for the fact that it doesn't seem to run at a constant powerlevel. I'm thinking that it may be an injector or possibly fuel pump adjustment. Any help will be much appreciated.