Hi guys .. i'm running ABF engine with the following - AMC Gearbox "wire" 020 - KR ECU and wires - new Bosch fuel injectors - Bosch CIS-E fuel system "140" - Bosch fuel bump "please check the fuel pressure test on the link" https://streamable.com/6byd8 gearbox ratios is: FDR 1st Ratio 2nd Ratio 3rd Ratio 4th Ratio 5th Ratio 3.66 3.455 1.944 1.286 0.969 0.805 gear and roadspeed 1 2 3 4 5 34.6 61.5 93.0 123.5 148.6 "stock by mph" 60 120 160 200 210 "mine by KM" the issue is ... the 5th gear set on 5100 RPM MAX, which reach to 210KM MAX ... other gears running prefect ...best ratio and max rpm as i tested and wrote it down what would sizing or limit the speed for the 5th gear.
I had some similar problem, with a very similar set up, when i opened the engine, it was very damaged for knocking, on 4th cars revs till 7k rpm but very roughly on 5th not possible to reach more than 6k rpm, maybe you are running too much ignition degrees or too lean.
after searching and discussions it ended up with that the engine came out with all the power at the point and can be add more HP by anyhow to reach more rev. note the transmission 5th gear ratio can arrive to 240 KM, so you need to reach with your engine to at least 180 php to arrive to that KMs. that what i got too from a transmission mechanical. if you have any add kindly lets check it together