3-4 Slip Under WOT, Suspect TCC

[5.0L96Exp]

So I have made several upgrades to the 4R70W in recent months (she has 250000km on her) and I have recently noticed that during WOT accelerations from stop I seem to get nice firm 1-2 shifts but when I go from 2-3 I notice that the rpm drops from say 5000rpm to 3200rpm continues to climb to 3300rpm then slowly falls to 3000rpm then continues to climb back up to 4500rpm before shifting into 4th gear. However, the vehicle is accelerating in 3rd gear at a fairly fixed rate. I suspect that the torque converter is not locking up in 3rd gear. To test this I tap the brake pedal at apx 50mph under medium or no engine load, not enough top slow the vehicle, I expect that if the TC was indeed locked that it would unlock, rpm would jump by 100-200 for a second or two then fall back down.. But I see no change in the rpm. This leads me to believe that the Torque Converter Clutch (TCC) solenoid is bad. The catch is that I'm also running on 33's and I know that my speedometer is off by 10mph or so despite having changed the speedo gear in the transfer case from 18 tooth to 19 tooth (it got me closer to actual speed anyhow). I know the PCM relies heavily on both the Output Shaft Sensor (the OSS located in the 8.8' the gear) and the Vehicle Speed Sensor (the VSS located transfer case). Also I have installed the Bauman shift kit + new 1-2 and 2-3 accumulators and am running some el-weirdo Quaker State Universal Mecron 3/5 ATF... So the question is who is the culprit.

Is it my weirdo ATF. The Baumann kit is pretty solid, but maybe I didn’t torque the valve body down tight enough. Or maybe after 250000km my TCC and EPC need replacing.. This problem is hurting me at the pumps. I cant get more than 300km on a tank (used to get 400 a few weeks ago).

 

[5.0L96Exp]

Oh and I checked my fluid levels and they are A OK.....OD works fine too.

I was thinking of hooking an LED+1Kohm resistor in parallel with the TCC to monitor when the PCM attempts to lock and unlock the TC. Is the TCC in any way pulse width modulated or is it simply on or off (ie 0 or 12volts nothing in-between)?

On a side my original Timkin wheel hub just bit the dust with 250000km on it.. Not bad if you ask me.. If I was rich and thought the rest of the truck was good for another 250k I would definitely go Timkin again but given the price I think I may try one of these cheepo wheel hubs of ebay for 100 bucks instead.. Well see......

Update: So I ended up going with an SKF wheel hub.. its no Timkin but they had it in stock at Canadian tire (go figure.....) for $248. By the time you add shipping, tax duties etc a $100US China made ebay hub ends up costing 200Cdn.. so for another 50 i figure go name brand... Replaced in less than an hour with a 8mm, 15mm, 19mm and 1.1/4" sockets.