Carburetor choice

Did you do any tuning?
Did you get it up to 60 degrees or more?

In my manual-trans car, which is geared at 65mph =2240rpm; every 3 degrees added at 60 mph, will produce a 1 to maybe 2 mph speed difference, beginning at about 50 degrees, and going to 63* the highest I have tried. With the more speed from the first 3* to less speed on the last.
What this means, of course is that to maintain my speed, I get to close the throttle. And with the more closed throttle, I get to take fuel out, and thus decrease my fuel consumption.
Now, per the math, this is 13* additional timing, or 4 increases of 3*, and so a speed increase of perhaps 6/8mph; that's about 10/12%. I would and do, call that tremendous.
Your results may vary.
After all, I run an 11/1, 367 with a Commando/GVod manual trans, and a 230/236/110 cam, and my cranking cylinder pressure is already 177psi or more.

But if you are cruising with 3.55s then your rpm is likely to be about 2900 with 27s and at zero-slip ; say 3020 at 4% slip. At this rpm, with a good working VA, you might already be up to near 50* of timing. The efficiency of the engine at this rpm is very significantly better than at 2240 , and it may not want much more than 50 to 56. And so it will be very difficult, if not impossible, to see any difference, unless you can change the timing on the fly.

As for Torque at Part Throttle, the only time the VA is working; You have to be able to adjust the timing while driving, to experience the difference. Otherwise you are just driving deeper into the throttle. AND, you may not see a difference on a vacuum gauge; the divisions are just too gross.

The goal of all timing devices is to put the peak cylinder pressure at or near 25 to 28 degrees after TDC. My Vcan has been modified to bring in 22*. If at 2240rpm this takes 56 degrees, and my V-can is at 22*, then the rest, 34* has to come from the Power-Timing. Since at 2240 rpm, my mechanical is only 24, I'm 10* short. But, I have a dash-mounted, dial-back, timing box with a 15* range............. so I'm good to go.
So unless you have played with numbers this high, on the fly, I'm not surprised by your results.

Here in Manitoba,
our 87E10 gas is up to 1.39C, per liter yesterday.
=5.06 per USg in Canadian Dollars
My Barracuda with a 223/230/110 cam made over 50% better freeway mpgs than city mpgs and on one certain test-trip made nearly double. Now granted,not nearly all of that was due to the VA; never-the-less, I am talking 10 mpgs or more difference. With a 66 liter tank (~14gallons Imp), that comes to 140 additional miles per tank, at the very least; that cost me only time in the tuning, to get. How much of that is ONLY in the VA I cannot say, butum; I'm still calling it; "tremendous".....