A-833 2.47 1st gear change to 3.09
I would change the rear gear, or figure out why the engine won't pull off the line. Here's an example. In the 70's I swapped a bone stock 71 (high compression) low miles 340 into what was my 70 440-6 RoadRunner. You are talking about a fairly heavy car, the "hemi" 18 spline box with a taller 1st gear, and 3.54 Dana. I had pretty tall rear tires, and it ran about 3000 at near 70 mph. I never had any trouble pulling away from a stop and as I was in the Navy for part of that, I ALWAYS had two heavy tool boxes and other junk in the trunk. And even though it WAS a bit of a clutch slippin' operation, I pulled a trailer with a 70 Cuda on it and full of spare parts, when I got out of the Navy, from San Diego to the N end of Idaho.
Maybe the cam isn't timed optimally? Carb jetting/ ignition curve? Makes a lot of difference
I've always figured the 3.0 first gear is a weak sister. If I remember, the main shaft is smaller