The Hitec Eclipse with a standard Supreme RX will work admirably in your gas model... Of course this is providing your not introducing in stray EMI/RFI, that said do NOT use a PCM RX to solve your problems.

As SiliverSurfer suggested look very closely at the engine installation, specifically the ignition system. Look for metal to metal abrasion, loose or not completely seated spark-plug and plug wire boot, fouled sparkplugs, Resistor type plug, damaged or loose ground conductors.

Make sure NO additional ground cables have been introduced, the only correct method of grounding the ignition system is provided via the module directly to the engine block. In most cases the sparkplug wire is shielded or contains a braided wire mesh which either encompasses the high tension lead or is a separate cable all together, one end is attached to the module and the latter to engine and or sparkplug base.

I’m assuming your ignition switch and battery is separated from the rest of the radio system i.e., an independent system and there is some physical distance separating them as well?