5.9 magnum and the ax15

If you're bound and intent to put a five speed in it, start looking for an NV3500. The smaller NV is not bulletproof behind a 5.9 by any means, but the AX15 was not offered behind any V8. The best NV would be a HD dakota unit rated at 340 lb/ft of tourque, but the 4:1 first gear is a bit much for a street car...