Don't really want to cause any major controversy but not ALL T5's will work with a 3.08. S10 T5's come in basically 2 configurations.....the .86 OD model with a 4.03 1st gear that will work with a 3.08. This transmission is normally found behind the 4 cylinder S10 engine. As Waldo pointed out...you shift out of 1st gear VERY quickly.
The second S10 T5 is the .72 OD from behind the 2.8/4.3L V6's with a 3.76 1st gear that WILL NOT work as a 5 speed with a 3.08 R&P. REPEAT...WILL NOT WORK AS A 5 SPEED WITH A 3.08 R&P with a 27-28" rear tire. As proof I have an 88 IROC-Z 3.08 posi/disc that I was told would work, collecting dust in my shop.
The 235 makes it's power between 1600 and 2400 RPM's. I've found over the past 8000 miles, that the engine is happiest in the 1800-2200 rpm range. After the pricey 3.08 debacle, I settled on a 3.42 89 Camaro diff which works great. Cruise at 70 mph is at 2000 rpms, there's plenty of throttle/mph left and you can drop down to 45 mph in traffic and accelerate without a downshift. First gear is short and you can cruise in town in 4th gear at 35 mph with no lugging. If you lived in an area with long hills you might even want to run the numbers on a 3.73. It would let you cruise at 55-65 mph at 1800-2000 rpms which might prove to be more comfortable in your truck. The 3.73 62" wide Camaro diffs aren't as common as the 3.08's and the 3.42's.
You didn't mention which T5 you have.....it'll make a BIG difference in whether your 3.08 diff will work as a 5 speed or limit you to the first 4 gears. To identify your specific mechanical speedo T5 you need to have a small tag with numbers that start 1352-xxx-xxx. The numbers cast into the case will not identify the ratio. If you're really lucky, you'll have a paper barcode label on the top cover that will let you ID your ratio. If you have neither.....send me a PM and I'll fill you in on how you can quickly/easily determine the ratio.
I hope this helps you sort out a few things with your T5 swap. Without a doubt it's the best upgrade you can make in a Bolt. Being able to cruise at highway speeds effortlessly, makes the modification worth the effort.
Dave
