A4LD tranny problem. Tranny slips when cold, most often not engaging in low (reverse is fine; so far no issues at all in reverse). Sometimes problems from 1st to second. Usually when warm operates normally, though occasionally will slip. I have dropped tranny pan, replaced filter, cleans thin film of gunk from pan. Found no chunks or pieces, just fine film. Replaced drained fluid with Mobile 1 ATF. Old fluid looked pretty good. Next, added external filter. Then used the disconnect tranny line & pump out fluid into measured gal jug one quart at a time, replacing 12 quarts with Mobile 1 ATF. Next, followed method of tightening bands in other posts on this forum. Loosened lock nut, tightened bolt to 120 in/lb then backed off 2.0 turns. Did both front and rear bolts. After this work, tranny still slips. It seems like problem actually got worse after doing all of this. Searching seems to indicate valve body kit/replacement might be next. Have read this may not be fully beneficial without a tranny rebuild. Any ideas? Thanks.