Check out Bud's threads.
http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=13040
http://www430.pair.com/p15d24/mopar_forum/showthread.php?t=13524
1st Gen is 87-96, 2nd Gen 97-2004, Gen 3rd 2005 to present
Though there is debate as the begining of the second gen being 92-96.
Offically there are 3 generations, but read this from the disscussion section of Wikipedia:
http://en.wikipedia.org/wiki/Dodge_Dakota
"No, there are 4 generations. The 87-91 only share the cab and bed with the 92-96. Suspension upgrades, a different engine family, completely different electronics, etc etc............certainly there aren't a bunch of seperate Gen 1 and Gen 2 truck clubs based off of those body styles for no reason. Also, any R/T owner will say his truck is a Gen 3, and the few people that own the latest body style agree they are Gen 4's. Theres an old saying...........if one person tells you that you're wrong, you can laugh and ignore them, but if 100 people say you are wrong, its time to correct yourself."
Devilbrad, owner operator of www.devilbrad.com an all late model Dodge Truck community and Dakota enthusiast since 1987.
They made the engine compartment bigger in 91 to fit the 5.2.
Seems a 92 or 93 would be a safe choice for a 48 Dodge.
48D