As long as you are receiving Data Packets (CMR's @ 100%) there is no need to even look at the the radio.

I have worked on a SPX 4420 (Brand New) and a 3310 (04 or 05) this past week, 4420 Insight 5.1 no issues at all worked great. The 3310 is another story (same as yours). I'm about 90% happy at the moment. use NavII firmware 4.51, and try swaping the autosense. on the 3310 I found a happy medium at 12 for PGain, 48 for Left DZ and 45 for Right DZ, but every sprayer is different, You also might look at the line acqusion and make sure it is not too high. Good Luck these sprayers can be a handfull. On the hydraulic side make sure that you do have the Pressure Relief set right, start by checking the Pressure relief on the machine then set the valve accordingly, I did have to change the relief on the valve. Let me knof if you need help doing so.