The GVWR of the 2010 Montana 3400RL is VERY close to 16,000#, I have one. You do not deduct the pin weight when looking at these numbers. Specs are on the Montana web site. If you are looking to upgrade the tires you could go with the Goodyear G614 like many other Montana owners have done, you could also look at the Sailun S637 which is also a G rated tire and quite a bit cheaper. The rims should be rated for the 120#psi as mine are but you can check by looking on the back side of any of the rims. There will be a casting mark on one of the spokes listing the max psi for that rim. Your camper is equipped with the 7000# axels also. Tim