transmission and control elements of the radio are separate, it takes PPM modules, like many others old and new. the frsky is exactly that, a PPM module. For £20 (module) and £14 (receiver) you can try it out far cheaper than and new TX. you don't even have to permanently fit it to try it out.
firstly identify if your system works interference free on your bench. you cannot rule out a new receiver as not the problem. its new therefore untested by you. did you test with another ko 40mhz receiver on the day?
secondly, ensure your sticks are not worn out and are working accurately on 40meg.
I've done many frsky conversions, and think they are very rhobust and reliable and give a new lease of life to old kit.
__________________
-------------------------------------------------------------------------------------------------------------------
Team Yokomo - YZ-2CAL3 | YZ-2DTM3 | YZ-4SF2 | YZ-2T | YZ-2DTM Worlds | YZ-2DTM x2 | YRX-12 x2
-------------------------------------------------------------------------------------------------------------------
10electric | Batley Buggy Club | YORCC | RHR | MB Models
--------------------------------------------------------------------------------------------------------------- |