The hell with it, I say do it! You're right about value, the SRT will hold it's $$ much better over the long run. Plus, do you honestly think you'll ever regret trading your truck for anything with a viper engine under the hood?
But yeah, from what I remember, the 2dr trucks got the manual trans and they were not rated for towing or much payload in the box. However the 4dr's got the auto trans and were rated for a useful amount of towing/payload. Afterall, it's the same trans as the automatic cummins trucks get.