No problem.
What's it doing that makes them think it needs replacement? This is very low mileage for an Allison. There is one thing in particular that you have to avoid, which is driving with the ABS light on. This causes the torque converter to unlock, and the trans overheats.
When i condemn a transmission (vs fixing/attempting to fix it), it's either because it's full of metal shrapnel, It has active codes showing incorrect transmission ratio (it commands a gear but a burnt up clutch pack never reaches the rpm the tcm expects) or when there are recurring codes for turbine or output shaft speed, caused by excessive radial movement of these parts, suggesting bushing failure. These are the most common things I've seen.
What sort of truck do you have? What wheelbase? If it was incorrectly spec'd by a body builder, or has some unusual configuration, the driveline angles often need to be adjusted, usually by replacing spring perch blocks on top of the rear axle. This changes pinion angles. A 1-3 degree adjustment is usually all that's required to get it correct. An incorrect pinion angle wears specific bushings in these transmissions (1000-2000 series Allisons, anyway), and the problem will reoccur if it's not addressed.
If you tackle it yourself, I'd recommend getting the books so you have specs for bushing measurements. This is critical. Without this being right you'll waste time and money. The books are also well illustrated and broken into modules so it's easy to understand and you'll be less likely to make mistakes.
