Regarding my can of worms comment: gas for diesel can tow your current TT. That question is irrelevant. There are well documented already discussed compromises when choosing one or the other. The useful discussion was linked.
Reality check: You sold a $20k vehicle and are shopping for a $50-80k vehicle in order to save $100/month in fuel?
Regarding your stated 10-12mpg from the prior TV - was that towing or your 90% daily driving miles?
Just to play along, these are what I understand are your not directly communicated requirements:
Payload at least 1500 pounds, 1800 better
SUV shape
XXmpg mixed daily
YYmpg towing
The only significant way to improve upon all the concerns you had with the Sequoia is the 2001-2003 Ford Excursion diesel. If 10-12mpg was you city/90% driving, then nothing short of a hybrid electric GM SUV would significantly exceed that. In our "city/daily" driving with a 3/4 ton Suburban we get 13-14mpg. You got less in a half ton, so your city/start/stop % is far higher than ours.
You are a prime candidate for 3rd/dedicated TV. Get your favorite Prius for DD for $25k and a $10k 3/4 ton truck for towing only. Why would you need to store all 3 vehicles in a garage in California? Do you have a driveway too?