Drawing on what I said to a similar question:
1) In general people do not maintain the TM. If you stall or reach the point that you should not increase the TM, then you should decrease it. Generally, people just go back a few cycles then try to set new rep PRs and such. You can also do what Wendler has said about 5 forward, 3 back to reset before you have to.
2) If you are at minimum reps, you should reset. From Wendler's recommendations for different particular programs, you should typically be able to get 5, or at least 3, solid reps with the TM itself. So, I would reset to a lower TM rather than increasing it. In your case, you know what weights you are and are not able to get 5 reps on, so you can just set the TM to the weight that you were able to get 5 solid reps with (perfect form and good speed), or lighter. Set new PRs at the lighter weights and work your way back up to the weights that are currently sticking for you. If you still stall after that, reset again and try a different variation of the program (e.g., change the volume of the supplemental lifts).
3) Wendler also has new recommendations about the TM that have been touched on in the forums and are to be spelled out in the new book. Basically, he has programs of 3-5 cycles, with testing and resetting of the TM between programs. I will not attempt to spell it all out, but perhaps someone else will.