Martin,
I'm a bit mystified by your problem, obviously you are well aware of the shift issue and would well expect the positive shift receivers to work with your new JR tranny, by any chance have you tried using your old (Airtronics, I assume) tranny with the new Jr Rx to see what range you get? The only other thought is whether the JR Tx is a bit off frequency, only a repair facility can check that, one other thought, I assume (I've been doing that a lot lately
) those other Rxs were always on ch 50, or have you been popping crystals??? good luck,
Pete