Prepairing for towing

[mega]

I'm thinking about selling our f150 that sits in the driveway and costs me money, and prepping our 2001 x5 3.0 for towing

any weak points on the x5 for towing? Transmissions up to the task?

Will be towing a 4000 pound trailer and camping gear, I get 12mpg towing it with the f150 currently

I have an aftermarket hitch with a bar that reinforces it up under the x5, I use the x5 with a motorcycle carrier (high tongue weight) to haul my xr400 and ktm 200, lot better mileage than trailering it