You may want to find a factory service manual to pursue this probable antenna diagnosis. A 3' length of wire as a substitute antenna can help find where the break in the signal is occurring. Reception should be acceptable on clear channel (50kw) stations ~50 miles away.
Start behind the radio connecting to the center pin and hang the wire out the passenger window. If reception is strong, the problem is towards the back window. Some disassembly of interior trim may be necessary.
Antenna modules (amplifiers) can fail, but confirm this first. Make sure that 12 volts and a good ground is present at the module. The antenna grid printed on the glass can be repaired with the defogger grid repair kits. Being in the cargo area, sometimes an object can scrape and open the glass antenna and defogger grid.
If reception is poor with the engine off, the spark plugs aren't the cause.
I don't know about the pistol grip fit, but maybe a shifter is out there that would work.