With the changes I made to our duct work and vents, both our thermostats are staying within +/- 2 Degrees.
I am ok with that range between the two.?
How did they tell you do not have the U at the end of the duct, do they have a bore scope of some type.
I know our front duct runs quite a bit past the last vent in the ceiling, just do not know how far forward.
Guess if it just dead ends it would be a good idea to cap the duct off after the last ceiling vent.
Robert & Sheryl
2014 Redwood 38FL
MoRyde 8K IS, Disc Brakes, MoRyde Pin Box
17.5 Goodyear G114's, RV Armor Roof
2018 RAM 3500 DRW, Curt Q24 Hitch