I'm building a tow rig out of a 95 TopKick with a 3116 Cat and an Allison 545 tranny. I'm looking to re-gear the rear end with probaby 3.70 gears to get some speed out of it and turn up the Cat to 250-300 HP which will be too much torque for the 545. Does anyone do upgrades to these tranny or is there a drop in replacement with more strength? I'm looking to tow a 20,000# boat around the country. Any help would be appreciated. Thanks.

Any idea what torque you will end up with? I looked at the allison website, not sure if the 2400 is big enough or not. You may need to go with a 600 series like a 643. I'm not very familiar with their newer electronic models.