ok i have been getting poor mileage (best 17mpg) out of this '96 dodge 2500 money pit i have bought i just did a topset which should make a difference, (intakes were good but exhaust were at or over .025) but i think my convertor is not locking.

warmed up doing 50mph if you let off throttle rpms go right to idle. a locked converter rpm should drop slowly and give slight engine braking till you hit the brake and cause it to unlock in every other vehicle ive owned. is this just a 47re thing or do i have a problem? if this is wrong how do i troubleshoot? thanks