Put in an Eaton five speed instead of standard Dodge tranny.

 

I would do it if it is a 4x4, however, if it is to be a daily driver I'd consider a turbo'd 5.9 12valve with an automatic transmission with xfer case. I have built diesel drivers from the late 60's to present, stuck a 3-53 Detroit into a 1952 GMC panel with a modified cab that resembled "RESCUE 9" from the TV series.
The 3-53 got pulled and in 1974 it went into a 1964 Jeep Gladiator ahead of the the original Jeep trans. To do this install, a 4inch lift between axles and springs was needed to just make up the difference between the center of the crankshaft and bottom of the block. I ran with the Jeep five lug sixteen inch wheels running 7.50 X 16 rubber. This combo gave me 60 mph at 2800 rpm in direct (4th gear), as for pulling it was nuts.
In 1979 gas hit $0.66/gal in Hawaii and I thought it was the end of the world, I had a 1975 Ford F250 4X4 that got about 9 mpg with a 300cu in six. I did a re-power using a Perkins 6-354 in-line six coupled to the Ford New Process 435 transmission for 128 ft/lb of torque at 1400 RPM.
On all of these conversions the big factor was good old "common sense", I never had a screwed clutch or twisted drive shaft, well except for the jeep.
With the Jeep I fried the clutch pulling a trailer with a small CASE track loader from sea-level to above 2600 feet, clutch failed at about 1800 foot elevation.

As for the RAM 1500 I'd keep the original axles with 5 hole lugs and I'd learn to drive by feel. Good luck, - Bill

 

Here is probably your best option...Sell what you have now, and buy a 2500 diesel, much less of a headache down the road!

 

Exactly....

Not to mention, they're getting cheap now!

For those naysayers, who constantly argue whenever anyone throws reality into the picture in some manner, I simply would communicate the following. Please re-invent only wheels that need re-inventing.

Otherwise, do something original. It's your choice and $$$$ in the end!

Cheers!