Take a close look at your incrementals. They should tell you where you are loosing ET. Back track from there, in otherwords confirm where it is loosing the ET.

You say it feels like it will not pull up top but do the incremental times show that? Or is the problem form the get go. If it is that you are loosing ET the entire track I would be looking close at the converter or trans itself. Maybe pump pressure is being affected as the trans heats up? Know where it is loosing the ET will help diagnose where the issue is. Takes a BIG problem to loose that much ET on the top end of the track. I suspect it will be found elsewhere.