My buddies 97 ram 318 2wd has been having a little issue. When cold outside around. Freezing if he just jumps in And take off when he gets to the top of the hill and stops and then goes again it'll slip. It revs for 2 seconds or so then goes. After that it wont do it. Only when its stone cold . What would cause this? Filter has about 15k and flush was done with bg universal atf . The fluid says it is specd for atf3 and 4 . The fluid looks good it goes into each gear with no delay or issue.. someone help thanks guys..