I have 2009 Tacoma with trailer tow package rated at 6500 lbs. I am looking at trailers in 4200-4500 lb range. Assuming I try to avoid carrying lot of water in tank, and have around 500 lbs of gear I should be around 5000 lbs and well under the 6500 limit. Also tounge weight would be around 500 and I have 650 rating. if I go to the Rocky Mountains should I expect problems with steep grades? Should I get truck wiht V8 with say 8000 rating?