I am using a G5RV and an Icom 756Pro II. The auto antenna tuner will
tune the antenna fine except in the area of 3963.5 and up to at least
4.0385. I use 4.0385 as a member of MARS. Right now my SWR "as
shown" is well into the "red zone".

Is there any way to modify the antenna to get it to be a better match
so that the auto tuner can do its thing. The antenna is the shortened
or Jr. version with a ladder wire lead in.

Would changing the lead in to RG8 coax be a help??

Sure will appreciate some help. I am a novice at this and it is
important that I am able to use 4.083.5.