Xb8 modem wont get past 5mb speed but my xb7 get full 1100 out of 1gb

Please help fix my file as a technician already came and only wants to downgrade to x7 witch worked great but I want the x8 I have and don’t want to downgrade I also should mention that I have a working x8 its just not connected right and need a level 2 to fix it