Have a 41 1/2 ton 3 speed. Transmission has been rebuilt using all nos gears. Problem is it will not stay in 3rd gear under acceleration most of the time, feels like it is being pushed out of gear. It is going all the way into gear and shifting feels normal. Have pulled the top off the tranny and everthing looks fine as far as gears engaging. I am getting ready to pull the tranny back out, any sugestions would be appreciated. Thanks.