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I can still shift tho but my thumb is always gripping to help me press the strings and all.
"Gripping" That word makes me think you are holding onto the neck to tightly. There is a difference between gripping and supporting, but that is not something I can explain with words on a forum.
The key is in bunify's use of the word "always". Change that to "when it's necessary", bunify.
An important thing about shifting is anticipation. If you relax everything more and only grip with your chin when you are about to shift and relax your thumb even more when about to shift, etc.
Maybe you could use shifting exercises as a way of developing more relaxed playing?