Are you using an AF meter? How's the ignition and what are the timing settings? Does it have an adveance curve or locked out.

5 seconds... really.

None of the 850 or 950 ultras I've dealt with had much in the way of tuning issues.

The 80496 950hp's are horrible on cruise and require major tweaking to get a decent A/F.

IMO, you aren't going to find anything out of the box that will perform spot on. Everything will require some tweaking. It's not a box stock 375hp 440 where the dealer has a carb on the shelf that runs on thousands of them out there.