Quote Originally Posted by 632 Regal View Post
When I got the EAT chip my 5HP18 would rev neutral between shifting 2nd and 3rd. Would slam so hard the Trans would have blown if I didn't swap it right out. This was on mild acceleration only, full throttle shift was fine.

The stock engine chips cut the engine momentarily between shifts so they are smooth. Doubt it is your problem but throwing it out here anyways.
Some of the 5HP18s had a fault with 2-3 shift 'flare'. Mine did. You can solve the problem with the '2-3 flare correction kit' 5HP18.SK01. It is just two new springs you replace in the valve body. But it works