i have been trying to fix this for days now. i have a jetpack 890l going to a netgear range extender wn2000rpt v2 then (by ethernet) to a seperate d-link router. it is hard to get into the d-link router but after several attempts it let me in. i then put my xbox into DMZ(de-militarize zone) and opened all four ports. the d-link router was used before when i had att dsl internet.
the jetpack has no UPnP and when i port forward thru the jetpack or dmz thru the jetpack nether would work. i called both xbox and verizon but they couldnt figure it out. i suggested i try the above idea and the xbox support person said it may work. and it did.
if u are use a wireless adapter or an xbox with wireless i suggest getting a wireless router and link it to the jetpack. this was the only way i could get mine to work. just make sure it is a xbox live compatible router d-link has served me well for years but netgear make some also.
I hope this helps!
P.S. THANK YOU Amilia(maybe misspelled) from xbox tech support for trying so hard to fix this when verizon tried to pass the buck.