I am new to this forum and hope I can get some help. I just finished building myself a K2 Animal (98 frame) with mostly new components but I re-used my old shimano 7sp drivetrain (ran out of cash). The drivetrain has 4 seasons on it. I did replace the chain with a new shimano IG chain. The original chain was an IG also. On the stand, everything runs perfectly smooth, as well as on the street, as long as there is moderate to no load. As soon as I apply some heavy torque, the chain skips at the back end. The chain doesn't appear to be coming off the cog at either side. It almost looks as though it is literally skipping a tooth. I can get this to happen on the 11, 13, 15, & 18t cogs. I didn' t try on the bigger ones, I would need to be on the trail (or at least a hill) to maintain any torque. I would greatly appreciate any help.