Pepwave Max Transit CAT 18 with TP Link Deco M55 Mesh System in Motorhome

Please forgive me if my questions are very basic. I have been using a Max Transit Cat 18 connected to a 7 in 1 Parsec Husky Antenna for a couple of years, Using Wifi as Wan was fine, but we were experiencing buffering while streaming TV at various times. The RV park wifi is usually between 6-30 mbps download and 3-8mbps upload per Ookla speedtest. As you can see it is all over the place. Using my sim for Verizon, It will be 50-100 mbps download and 3-5mbps upload; again using Ookla. I will see buffering wether it is in Wifi as Wan or the cellular signal. I had an old Deco M55 Mesh system from home so I thought I would try using it in the RV. One of the Decos is connected to the Pepwave via ethernet and acts as the main unit. I have two other units, one at each end of the RV. We still experience buffering at various times even though download speeds to the pepwave are good. I have the Decos set as AP units and the Pepwave as the main router. I have the AP as on in the Pepwave administrative page, so that I can access the page and make changes from my phone. Could that be interfering with the Decos and causing the buffering? Would I be better off to purchase a Pepwave AP one Mini or the AP AX lite and just trash the Decos?
The other issue is understanding using Wifi as Wan. I have a setting for 2.4gHz and another for 5gHz each using the RV parks bands as the Wifi source. Can both of these be set for using them together in Priority 1? I would use my cellular plan, but it is limited to 150GB.