my 99 f150 4.6 2-2 runs and pulls normal when its cold.when its hot it feels like its going in and out of gear you stop at a light it feels fine then you take your foot off the brake push on the gas starts to take off then slams in and out of gear or something started doing this month ago or more now i'm starting to feal it when its shifting to second pulls good once its in gear changed the fluid and filter changed it again a few days later not much help OD works fine so far reverse is fine no codes in the computer what can this be thanks for your time merry cristmas