94 3.1 Transport no get up and go

I have a 94 3.1 Transport not sure of mileage or any other details as vehicle is not in my posession. If just driving around town at low speeds its fine but when you step on gas it lugs down and will not go over 30 mph. No chk eng light or codes. Vehicle sat for a couple years and all fluids have been flushed and changed and has clean fresh gas. Any suggestions on where to go? If any more information is needed I can get it.
Thanks for the help
Bruce

Backpressure test?

WOuld go as usual and suggest verify fuel filter, but not convinced....What if you try to accelerate slowly..? Fuel pressure with the TBI is supposed to be near 12psi. <I've never seen blocked catalytic problems with the TS but quite often with KIA Sportage...my other car....so it comes to my mind....but just like that....
I'd rather suspect sensor problems....throttle sensor, pressure sensor....

http://www.avigex.ca/xport/fuelcontrol31.jpg

Lots of diagrams available at my website www.avigex.ca/xport