Hi, I have a 2000 topkick rollback with a 210 hp 3126 cat engine and an at545 allison. I live in hilly country and need pulling power. I am going to go to a 330 hp 3126 cat engine and want to know what model allison transmission with overdrive and possibly a retarder will be needed to accomodate the extra power. The main reason overdrive is needed is because I went to a 3.90 gear ratio to try to improve power with the 210 hp but my top speed is now only 62 mph. I do not want an electronic transmission that has to interface with the engine. Can someone please give me some advice. Thanks, Frank