I just took my 55 sunliner on its maiden voyage with the 351 and C-4,the trans is a junkyard purchase and it took a while to shift into third and did good on the first and second time it went into third but now it will slip a little before going into third but does not slip while in third. Is there anything I can do to it or just drive it a while and see how it acts as the trans has probably sat a few years,before I installed the trans I installed new seals and filter and new fluid.