get under there and look,could be any of the seals, but I just had problems with the lines going to and from the tranny cooler the hose clamps were loose and I was leaking aLOT of fluid through that, after I tightened them up no problems, but to check look on the lower radiator hose and also on the drivers side fan shroud and look for tranny fluid/dirt builtup.

And once you get the fluid level to the correct place your tranny should engage much better, these trannies are really picky on the tranny fluid amount. But I bet your atleast 1 qt low or more to have those problems, fix it soon,
less fluid= more heat generated=damaged tranny
heat is our #1 tranny killer

1998 dodge avenger 4 cyl AT
Mods are:
Not enough