lots of h1's crack a cylinder due to overheating, there are aftermarket crossover kits to solve this. maintenance is key in a hummer, i recommend one that has seen the shop every year. look for a 98-99 for a better off roader at a good price. stay away from the earlier ones if possible. 99 gets tt4 and has abs. other common problems are pumps, abs modulators, and idler arms