T6 is the bin of the LED. Usually referring to an XM-L or XM-L2 LED. If it was a cheap flashlight, bought within the last year or so then it may be a counterfeit Latticebright LED.
Anyway, if you put a genuine XM-L2 LED in there you may see some improvement. It depends on what is in there currently. The stock driver should work with the new LED without a problem.
If there is sufficient heatsinking and the pill is not hollow I would recommend a new XM-L2 on a copper DTP board, with a new Qlite 3.04A driver.
Here’s a great source for tons of information on LEDs and pills and much more: