Given the discrepancy with the math a couple more questions.
Your RPM reading - is it on the factory tach or some other tool?
Speed - read off speedo or GPS?
2800 rpm in 5th, even with a 4 cyl T5 (0.79 5th) would be 4.56 gears in the rear.
Just looked up a list of T5s and ratios online. I found a couple interesting choices:
- A bunch of '80s S10 T5's have a 0.86 5th gear.
- A few pre-87 Mustang T5s had a 0.85/0.86 5th gear. (info taken from BritishV8.org)
1352-018 | Ford 1983-84 T-Bird/Mustang 2.3 L4 Turbo | C | 3.76 | 4.03 | 2.37 | 1.49 | 1.00 | 0.86 |
1352-034 | Ford 1983 SVO Mustang 5.0 V8 | C | 3.39 | 4.03 | 2.37 | 1.49 | 1.00 | 0.86 |
1352-067 | Ford 1984 SVO W/Hurst 2.3 EFI TC | P | 3.76 | 4.03 | 2.37 | 1.49 | 1.00 | 0.86 |
1352-154 | Ford 1987 Mustang/Capri 2.3 L EFI WC | X | 3.70 | 3.97 | 2.34 | 1.48 | 1.00 | 0.85 |
This is where the tag on your trans would be very helpful. A pic of the tag on one of mine sitting on the shelf...
Second row starts with 1352-xxx. In the above case xxx is 238. To me, that is the most important info when identifying a T5.