Your'e not looking for more power..... your'e looking for more low RPM torque. Your cam is the problem. That cam was made for the 340 when it had a true compression ratio of over 9:1. The main reasons to put a longer duration, slow ramp, moderate lift cam into the 340 was to stay with the lower lift for valvetrain reason, and the long duration at low lift made sure that the thing ran without detonation on bad gas and poor maintenance.
Switch to a different cam. Different gears are not not going to fix the low RPM dead spot, just cover it up to a degree and move the speed at which the car really rakes off to a lower speed like 25 mph instead of 30 mph. The higher stall converter will just let the engine rev up past the low torque RPM band when taking off, but it will lower fuel economy. (Dunno if that is important to you.) If you are drag racing this thing, then gear changes and higher stall TC changes make all the sense in the world. But for pure street driving, they will be just patches to cover for the wrong cam.
Your 360 has a true compression ratio of about 7.6-7.8. Put in a long advertised duration cam like that 340 cam in a higher compression 340 and it'll get past the low RPM's without too much trouble. Now, put that same cam into a low compression 360 and the DCR and the low RPM torque is just gonna go into the toilet. Take some cranking compression readings on all cylinders and I bet you will find them down in the 110 psi range, which is lower than a stock 360. So there goes your low RPM torque....
Look into a 256 or 262 advertised duration cam, with a faster cam ramp. Crane H-260-2, Voodoo 10200701 or 100200702, Racer Brown EH-8, or XE 256 or 262 are good candidates. All will have about the same or even a bit higher lift than the 340 auto cam that you now have, and the durations will be a lot shorter to boost up the DCR and the low end torque.
Right now, your DCR is down in the 6.2 range. That's bad juju for low RPM torque. As a point of reference for where your engine is right now, a really torquey small block will have a DCR in the high 7's range or better, and cranking compression numbers in the 140-150 psi range or better.
Change to a Voodoo 10200701 and install it with an ICL of 104 and now DCR is up to 6.8. That's getting better and your 360's longer stroke will help to work better with that DCR. The cranking compression numbers will be up around 125 psi now, not fantastic, but at least a bit better than stock. And these new cams will still breath at the mid and high RPM ranges like the 340 cam.
Work on the ignition timing after that to get it more advanced. That will help the low-mid RPM torque even more. (And if you want to do better yet for low RPM torque, you can mess with heads and head gaskets to get higher DCR and even better torque. But that is another level of work.)
Once done with the cam change to get past that glaring problem, and optimizing ignition timing, you can re-evaluate for the different gears and TC stall speeds.