I brought my TB in for ac diagnosis due to cooling stops in the heat of the day and while towing a boat. They claimed it was the clutch fan. This was replaced 3 years ago. They said it was not cooling the system properly with high temp and pressures the ac would shut off. Could this be true?

If the fan isn't working correctly the A-C won't work correctly.

Possibl,e but if they replace the fan and the problem continues now what, I'd get that straight first.

I would get that in writing and if they replace and it dont fix the problem then they refund your money or make it good.