I have all the same mods as you and also suffer from the dreaded 1/4 tank syndrome. I really don't think fuel starvation will be the issue if you are losing power at the top end. More probably a tuning issue or something electric or maybe even a vacuum leak as is the usual case.
I think I will have my mechanic remove and clean my fuel pump and fuel tank and see how that goes rather than pay over $500 for a new one.
As regards wheel spin the traction control should take care of that unless you have deliberately turned it off and are doing burn outs.
If I was going to put in a 3.0 litre motor I would import a fully re-built motor from the USA and then connect up the exhaust etc.
Hope this helps.
__________________
Owning a Cougar is like owning a Super Model
Good to own but "High Maintenance"
2000 Model Eibach Cougar (Auto) - Now dead & buried
