GX440 Cellular and Diversity

Hello all. I have a GX440 modem. We run these modems in Fire Trucks. We normally connect them via the cellular connection. I have one modem that if connected through cellular it reads 3g and reports a bad signal strength and the connection is spotty. Same cable, I take it and plug in to my diversity connection. It reports 4g and has a very strong signal. Can I conclude this has a bad cellular connection? We had a GX440 recently exhibiting the same issue. It was sent back to Sierra and they stated nothing was wrong with modem. Any help is greatly appreciated. Thank You

Antenna Recommendations:

Do not remove the diversity antenna. The diversity antenna helps the gateway achieve the maximum network coverage. The gateway works without one installed, but with reduced network coverage.