This may sound dumb, but are you sure you were in 1st gear? That also might explain the sluggish behavior off the line. I shifted at 4500 rpm and my stock Mav with a 302/c4 would top out at about 50 mph in 1st gear. That's with 245/60/14's. Taller tires may affect it but not by much. If I was still in 1st gear at 73 mph, I would be turning over 6300 rpm. Something sounds off.
wow why dont i ever see any nice mavericks around here racing ...,theres only 1 other maverick at our track ,now that mine runs 2 ....
You are going to LOVE that 3.80 gear. You will most likely just spin out if you don't have some sort of posi. But with my old motor, I used to go throught the 8th in second gear. Never shifted to 3rd until I passed the line. shifted at 4500 and sometimes as high as 5500. My new motor is a little better, but haven't tracked it yet. I still need an overflow can and tie down the battery in the trunk before they will let me run.