Separate a converter-clutch no-lockup complaint from a transmission that never reaches its highest gear by comparing gear commands, ratio math, and cruise behavior instead of guessing from RPM alone.
Drivers often describe both failures the same way: it feels like it will not settle down on the highway. But a converter that never locks and a transmission that never reaches overdrive are not the same failure. One leaves the expected gear in place but keeps converter slip too high. The other never reaches the intended ratio in the first place.
If commanded gear reaches the expected top gear but engine RPM still sits a few hundred revs high and converter slip never drops during steady cruise, the lockup branch becomes much stronger. P0741, P0740, P0743, and P2761 all support that story because they keep the TCC command path near the front of the graph.
If the transmission never commands or never achieves the top ratio, treat gear-ratio math and shift-control faults seriously. P0730, P0734, and P0735 fit better here because they question whether the transmission is actually reaching and holding the expected higher gear. In that story, blaming the converter first is lazy because the gearbox may never be handing lockup the chance to happen.
Both faults hurt fuel economy, but for different reasons. Missing lockup wastes energy through converter slip while no overdrive keeps the whole driveline turning faster than it should. That is why highway MPG is a useful support symptom but not a verdict by itself.
Capture commanded gear, actual ratio, converter-slip RPM, input speed, and output speed on the same cruise event. If top gear is present and slip stays high, stay in the TCC branch. If top gear never arrives or ratio math goes wrong, move toward ratio, valve-body, and shift-control diagnosis before calling it a converter problem.