Based on your description of hill climbing as compared to my '34 with essentially the same engine, I'd question if you have a high speed rear axle? The smaller Eights with high speed axles can be real dogs on hills. My '34 has the stock 4.69 and I climb all but the steepest hills in high gear. Obviously the price I pay for that performance is a lower comfortable sustained highway speed. So, what's your rear axle ratio, and what body style or weight?

I don't know if you are aware of this but it may be part of your problem. If you are still running the 726 vacuum tank fuel supply you must realise that if you hold the throttle fully depressed when climbing continuing grades, then you do not develop vacuum and you will start to run out of gas after about half/ three quarter of a mile of uphill grade. You should depress the throttle almost fully , if necessary, and back it off slightly so that you can still hear a distinct sucking sound through the carby. This will ensure that you are developing vacuum to refill your vacuum tank. A very similar situation to vacuum wiper systems on cars which do not have a vacuum pump. PT