I'm fairly new to this stuff but from what I can find the T5 should have a less than 1:1 final gear ratio so you will be running at a lower rpm than with your 3 speed, so it would be better for cruising, as long as your rpm's don't drop so low it starts to "dog out". If you jack the rear of the truck up you can confirm if the gears you have are 3.73's pretty easily by marking the tire and rear end yoke with chalk and spinning the tire one revolution and counting the revolutions of the yoke. When you know your tire size and trans/rear end gears, there are several rpm calculators (just google it) that will give you an idea of how fast your motor will be spinning. But keep in mind they don't account for vehicle weight, load, air resistance, etc.
As for the split rims, I have never had to deal with them.. but this might help.
split rims
