road car cam for my 318

I have a 318 in one of my Darts that is mated with a 42RH 4 speed OD automatic, and has 2.94 gears. 8.5:1 compression, Edelbrock Performer intake and a 650 AVSII. It is a long distance road trip car. I believe that the current cam is not serving me well - 17mpg on the road, lack of vacuum for power brakes at low RPMs, rough idle especially when in gear. When in overdrive with the lock-up converter engaged:
45 mph - 1550 RPM
55 mph - 1700 RPM
65 mph - 1850 RPM
75 mph - 2000 RPM
(all numbers approximate with relatively small tach and my 54 year old speedo (augmented with a GPS))

I'm looking for suggestions for a different cam. There used to be a ton of "mileage cams" out there in the late 70s/and 80s but I don't see them advertised these days. The one in there now is advertised for 1800 to 5000 rpms, so a lot of my driving between 45 and 65 mph barely gets into the range when I'm out on the road doing miles. I would like to boost the gas mileage if I can, and provide more vacuum to the booster for stop and go in town driving.