Tire Size

Ok all you experts out there. I finally took the baja up to the dunes here in Michigan and it did alright but....you have to rev it up to take off and when you shift to second you bog right down so I pretty much have to keep it in first. As you get to the top of a hill it just runs outta go. I think the problem is the tires. It came with 31-15.5 Terra tires which look cool as hell but I think they have reduced my gear ratio to much. The local bug shop says that those tires are also very heavy, requiring a lot of power to get em going. He suggests going to an aluminum rim and paddle tires to reduce the weight but thats a lot more money than I want to put into it.