I've started having an issue with a shift flare on upshift into 4th.

If i anticipate the shift and let off the gas, it shifts into 4th without drama. Otherwise there is a quick rpm flare, sometimes accompanied by a harsh shift.

I also sometimes get a harsh downshift into 3rd from 4th.

Truck is a 95, 460/e4od/4x4/4.10/8800gvw. Transmission was rebuilt at some point in 2005. I replaced the t/q last summer and replaced the solenoid connector. I thought the t/q was bad due to the excessive slippage codes, but after I had the trans out I was pointed to the connector which was in bad shape. That was probably the problem the whole time, but since I had it out I put the new tq in anyways. Also installed a transgo tugger shift kit, minus the pump mods as they appeared to have already been done.

Last summer I moved across the country, was probably flirting with max gcwr between the loaded truck& trailer. I did have to shut the truck down on a 9k ft peak on a 8% grade, I shut it down at 250F, indicated at the test port. Otherwise it ran a pretty consistent 225 or less. I'm running valvoline maxlife mercon v. The shift flare showed up after the drive, trans behavior was impeccable during the trip.

 

Sounds like the torque converter isn't locking up at 35 mph.

 

Converter seems to lock properly in 2nd and 3rd. It locks pretty quick after shifting to 2nd (in drive), there are 2 distinct events. It shifts and then it locks. In 3rd I honestly don't know how it works, it seems like it probably just stays locked through the shift, but I don't really pay too much attention to that one.

 

I don't drive this truck very often but I've been paying more attention. The t/c locks up shortly after the shift. A second or so after the 1-2, and pretty much immediately after the 2-3. The shift flare doesn't appear to be t/c related. It locks and unlocks properly all the other times without any issues.

It's been really cold here and with the trans staying at 150f and below, the shift flare has been less likely to occur.

Any other ideas?