My 4x4 extra cap 6' bed pulled our 7000 lb. TT from keys in Florida to top of Alaska and back getting 10 MG on freeway towing at 65 miles per hour in 6 it wood change to 5 on grades but that is the gear I should have bean in to start with. I newer had to get to second or have problems climbing any hill. Ran Florida to Texas solo at 70-75 getting 15.5MG return at 75-80 got 14.8 MG.
As said by others the MG from 150 to 250 is not that great, 05 F150 lariat 5,4l combined empty 13,5-14 MG towing 10. 12 F250 6.2l XLT combined empty 13mg towing 10. F250 empty a little les smooth ride can be bought for less than $40000 new.
Your Tundra can't be more than 8100 Lb all up including you and anything else loaded in and on it including hitch weight. Nor can you go over individual axle ratings. Load it op with passengers and anything else you plan on hawing in it take to scales and weigh it. Know you know what you have left for pin weight, allow yourself a little leeway and remember this is not dry pin but total including weight destribeting and sway bars. I hope this helps it is not a 100 Procent accurate as som weight gets transferred to front axle of tow wehicles and som to trailer axles so better to be a little light than to heavy
This is equipment supplied by sponsors,as you can se a film Crüe and backup wehicles and more than a dosen peaple. that trailer is about $100000. It is considered bad maners to drag a TTop that trach and diging it op as you are getting bogged is why more and more pleases are being made of limit to general public.