I have an 08 Tundra with 5.7 liter, TRD, 4WD tow package with the 6 speed tranny. The door jam plate will tell you what Toyota suggests are the vehicles max towing and weights. My truck is rated for nearly 11,000 pounds towing. I dont ever plan to come close to it. I will say it tows our heavy boat quite well and I am pleased with it.
As far a 5th wheel goes..cant give any meaningful input there...good luck.
Bob, Tonya and the kids
11 Rockwood Roo 233S
08 Grady White Seafarer 228
08 Tundra 5.7 liter 4x4 crew cab TRD limited
08 Toyota limited 4 Runner Iforce V8 full time 4WD, tow package