3.73 ratio might or might not work as well as you hope. The main thing is to determine what ratio chain you have in your T5. If first gear is 4.03 (as many did) I would suggest avoiding 3.73 and definitely avoiding the 3.90 or above. 3.73 will make your overall ratio a shade over 15. Your truck was engineered to have a 12.08 overall ratio in first. It was designed so it could haul up to 1000 pounds adequately. A ratio of 15 will mean you'll get about halfway through a city intersection before needing to shift to 2nd. The other common first gear T5 ratio will be 3.76 and that will make your first gear overall ratio a bit more than 14. Better, but the closer to 11.5 or 12 you can get, the more enjoyable it will be to drive.
As for your 5th gear ratio, if you have the .72 or .73 fifth ratio in the T5, then the overall fifth gear ratio with the 3.73 will be okay. It will pretty much mirror the overall ratio you'd have with a 3 speed with overdrive...2.66 or so and that will save you some gas money.
However, if you can find a t5 with the 4.03 first to .86 fifth gear ratio chain and a 3.07 or 3.08 rear end (look for a 12 bolt from the late 1960s) you could be doing well...particularly if you use 15 inch wheels and tires. With those ratios your 1st will be around 12.3 and your final gear ratio will be around 2.64 (around 2.70 with slightly smaller tires). By comparison if you had bought an El Camino with 235 and 3 speed with overdrive, you would have had an overall final gear ratio of 2.73.
Hope this helps.
