I have a 94 XLT 4x4 with 186,000 miles. It has the original A4LD transmission. The only tranny maintenance is fluid and filter changes at 76k and 167k that I did and a flush/fill and filter change by local garage at 184k. Before the last flush/fill and for the last 8 months the TCC lockup has been intermittent, locking up about 90% of the time. At times it won't lock up when all the conditions for lock up seem to be met. Sometimes it locks up normally and just cruising down a level road at 55 it will unlock for no apparent reason. It also will not lock up sometimes when it should and 5 minutes later, still cruising about 55, it will. I checked for EEC codes, both KOEO and KOER a while back and had none. I will check for codes again tomorrow. The truck also pings under load such as accelerating up a steep hill, not sure if this is related in any way. I have the ATSG manual for troubleshooting. The first step I plan for diagnosing the problem is check the TCC solenoid while driving. From reading the info in the ATSG manual it seems that the solenoid is normally powered, ie 12v flowing thru the solenoid to the PCM to ground. This allows the TCC to operate with hydraulic pressure from the transmission regulator system. If one of the TCC inhibit modes is sensed by PCM it removes the ground from the TCC solenoid and without power the TCC solenoid ports hydraulic pressure to unlock or prevent lockup of the TCC. Most of the inhibit modes are from sensors in the engine compartment. If one of these sensors is sending a bad signal intermittently to the PCM this could cause the TCC problem. I would much rather change a $25 sensor than a $1200 transmission. The Chilton's manual wiring diagram has a purple/yellow wire running from the TCC solenoid to the PCM. I've located this wire at both ends and hope/pray that it's the correct circuit. My plan is to cut this wire that completes the circuit from the TCC solenoid to the PCM and splice in my multimeter. When the PCM is not sensing one of the inhibit modes I should see 12v on the multimeter. If the PCM is sensing an inhibit mode then I should see 0v. I hope that this will allow me confirm or eliminate the TCC solenoid as the source of my problem. If the solenoid is causing the intermittent problem then I just have to find the sensor providing the faulty signal. Can anyone see any problems with my plan? I sure don't want to fry my PCM.