If hard shifts were his only complaint, the TCU can be recalibrated, the transmission can be adjusted to shift softer. Even most stock automatic transmissions usually need tuning in my opinion. A Ford 4R100 can be built to incredible strength and is also electronically tunable with equipment from a company like PCS. He can use a GM transmission like 4L80, or grab a 4bt with a turbo 400 from a bread truck, or an Allison 1000-though controlling it would be the challenge. He could use any year Dodge transmission, where there's a will, there's a way.