Sputtering and electrical

I have 91 w/a 3800 and all electronic dash, first the car has a problem with stalling with less than 1/2 tank of fuel remaining, it will restart but runns for a couple of km then stalls again , also when accelerating there is a backfiring sound coming out of the intake...next i recently changed out the battery in the car and since then i have no radio or heater controls, the heater control just shows"---" and the radio is stuck on one fm channel and the clock never changes ,any ideas would be greatly app..thanks for now....