Recently while shredding for quite some time on the higher frets I've noticed a slight discomfort in my thumb. It seems that the root of this problems lies in the thumb being a bit tense but I'm not sure. Since the neck widens on the higher frets I sometimes leave my thumb a bit 'behind' or as some say in hitchhiker mode. But I think this sort of grip considerably slows me down and reduces my hand span. To solve this problem I decided to watch a couple of videos of Paul Gilbert(whose right hand technique I have admired and copied) to see what he does. I found it a bit astonishing that he implements the baseball bat grip which I always thought flawed and 'incorrect'. Now I'm not so sure what to do. If anybody could resolve this problem I would be very grateful. Thanks.

P.S.: I'll try to post pics of my left hand grip on the higher frets.
I don't understand why you would view the baseball bat grip as "flawed and incorrect."

Some of the craziest, fastest guitar players use that grip regularly. While it may be harder to do 3-note legato runs with that grip or whatever, it is still a useful tool to have in your arsenal. I think that being able to switch between thumb-on-back and thumb-on-top is important.

That being said, I am definitely not one of those "technically proficient" guitar players. I just do whatever it takes to get those sounds out of my head and many times, it can be quite unorthodox. However, this is just my $0.02
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use what is comfortable for you, you should find that your thumb naturally falls into position whether that be behind the neck or over the top.

copying someone elses technique is the wrong way to go when it comes to posture as everyones body is of a different size and shape, watch other players for inspiration and musicality though.
If you want a clinic in fretting hand technique, watch Shawn Lane, it sounds like tension is your issue not your hand placement.
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