Post 5 yrs craniotomy for l frontal lobe avm & LP shunt. Lost 60lbs by gbp. Got 100lbs to go. Back pain that goes down right thigh. Any corealation?

Not to brain. I don't think they are related to your brain (avm or shunt) but definitively exacerbated by overweight. Likely you have sciatica or radicular pain.
Possibly. It sounds like you are losing weight intentionally. This may suggest back and disc disease which leads to the symptoms. With respect to the lumbar drain, there are rare cases where the catheter tip may be embedded again a nerve root. This irritates the nerve root and can lead to the radiating pain into the thigh.
Mri If ok with shunt. Get a MRI look for cause of leg pain disc herniation at lowest two levels not related to cramial issues.