no_6_oh_no

The ECU controls lockup by grounding the circuit for the lockup solenoid. Its possible it is a weak solenoid.

TH on your truck is just OD lockout so that should have no effect unless it is dropping out of OD. However, you will see a lot bigger jump in rpm when dropping OD and it will be noticeable. Definitely sunds like lockup is not functioning properly. That could be a mechanical issue or electrical.

teamroper12v

Ok, I have determined that it is not the converter unlocking. What I found is that the front band is loose. I talked to several trans shops today including some that have been recommended on here and all said that it is impossible for what I am experiencing to be caused by that, but it is and adjusting it has helped the problem. The new question is, can the front band be replaced without droping the trans? If so can anyone give the easiest way to get the band around the drum. Thanks.

dozer12216

The KD band in unapplied on shift from direct(3rd) to 4th (OD). Can have no effect on 3-4 or lockup IMO.
KD band cannot be replaced without pulling tranny. The anchor of band cannot make it around drum it rides against. The band is not worn out (generally) if there are still threads exposed above jamb nut.
Perhaps what you describe is not what is really going on. One more thing: Due to nature of OD direct clutch, one way roller clutch and overdrive clutch, there is gnerally no flare possible from third to fourth. Well if one way clutch was failed it would. Internet diagnosis is a big guess as you might have already figured.
I assume no metal was present during pan removal

UPDATE: After rereading all your posts, it is my opinion that converter is slipping when in OD lockup and hammering the throttle. Engine produces tremendous torque in condition you speak of, enough to slip a converter that has been stressed to many times. Sometimes the ATF additives have died and new fluid will restore clutch torque capacity before slipping. Could also be a front clutch slipping also. Did you ever council with Suncoast?
Again internet diagnois is difficult. If you take to any repair shop they gonna tell you it needs the works plus your favorite shotgun for downpayment.

no_6_oh_no

The front band is not applied in direct or OD, it is not the source of the problem. You have to tear the trans down to replace it.

Your symptoms suggest several problems. As dozer said a slipping TC could be the issue, or, since adjusting the band helped you may have a bad leak in the front servo. These are a problem area anyway so it would not hurt to look at it before dropping the trans. You can replace the piston with a billet one that has teflon sealing rings and check the bore for scoring. The pin will also wear on the cover and cause the same thing. It can be replaced with a billet cover that has an o-ring to address the issue.