The E4 and 4R are basically the same computer controlled tranny that you IDI'ers enjoyed in the latter years of your trucks. The E4 was in use in the 94-97 PSD's and the 4R was in the 99+ models. If you are doing some regular weekend type towing (RV, Boat, etc..) or just moderate towing for work I would definetly suggest going with a Sonnax, trans-go or FTVB kit to improve shifts and firm up some sloppiness, it needs a good cooler as well, the 6.0 tranny cooler was a good one as well as Tru-cool, check out Dieselsite.com for that. Russ mentioned the TC and that will probably be your most expensive piece but if you shop around you can find them for a grand or less, hint...click the UCC.com link in the sig behind my 95 specs.