Tim
This is a tuff nut.
Best option is to get it on a dyno and see what she is actually pulling - but if you have had the vehicle a while then your intuition is probably correct and power is down.

Cause well you are right it could be fuel even something stoopid like a fuel filter - do the easy obvious stuff and if no joy ensues get it to a reliable indy and get it gauged up.

__________________
NormanB
230 TE (W124) 1989 with 153,000 miles on the clock - hoping for at least another 100K