If its wheelieing you need to loosen the slipper off.
Get it to slip for a foot or 3 and youll be fine, add some lead to the front on the servo, or even look at getting one of the Trishbits/Ghea brass front bulkheads.
Add weight...get it heavy, back to NiMh weight and youll enjoy the experience. I remember when I went to LiPo and brushless in my B4 and I was scared whitless, now I love it
Ghea/Trishbits front and rear brass bulkheads,
Rudebits brass battery strap
Lead on the servo...