So, John, do you have a preference as to which controller replacement would be best? The inspire or either p3 controller?
I use an Inspire controller because I happen to have one at the time. I bought it in May 2015 to get the HDMI port, however right after I bought it DJI released the HDMI kit, which I bought for my Phantom 3P. So I didn't use the Inspire controller until I have my range issues with the P4. I think it's a better idea to use an early Phantom 3 controller (GL300A). I've heard others having good results with that. The reason it's a better choice IMO is:
1. They are cheaper than GL658A Inspire controllers.
2. They are easier to find on eBay. More of the GL300A were manufactured by DJI.
3. If you ever upgrade the antenna to a Itelite DBS2.2 (a common upgrade), you only have to deal with 2 antenna wires on the P3 controller GL300A. The Inspire has a 3rd antenna wire for the 5.8Ghz channel for a second remote. You'll have to add another small antenna for that, otherwise the 5.8Ghz RF transmitter will likely blow, rendering it useless if you ever wanted to sell it as an Inspire controller, or if you ever wanted to use it with an Inspire at a later date. If you didn't attenuate that 5.8 channel (installing an antenna) and that channel did blow, the controller would likely still work fine for controlling a Phantom with the other two 2.4Ghz antennas.