I have a 1996 F350 Turbo , in 1st gear it is sluggiush after it changes gears it picks its power back up and runs great , it does it every time and only in 1st gear , what could the problem be? It has been hooked up to 2 different machines and trows no codes , I have changed the whole exhaust,and serviced it completely, I am out of ideas , can you help me find the problem?