I recently had an issue with my truck's tbi conversion. The fuel lines had gotten too close to the exhaust and it was having boiling fuel issues. It would run fine until it got warm, it would always do it, but when it did it would stumble when you got to about 30%TPS. Idle was just fine though.

The other issue I ran into recently was on a buddy's truck, where the fuel pump was not making enough pressure at any state other than idle. The thing that tipped me off was that when in closed loop it was pegging max lean.

These are just my two recent discoveries with TBI. Were your injectors replaced with the TBI rebuild? Is their power wire corroded? getting hot? not able to carry enough current? Could this be combination of issues, i.e. injectors that get flakey at low pulsewidths, such as hot idle?

A datalog might reveal some interesting trends.