Timing problem

Bought a '96 Pontiac Sunfire 2.2L 3-speed automatic. Showroom condition, 90,000km from British Columbia.

Big Problem. Timing chain tensioner was gone and driven with out it for quite some time. Chain, tensioner and sprockets were replaced.

Transmission shifts fine, runs perfect at moderate speeds but under hard acceleration - well it doesn't accelerate. Slow and poorly, very rough, not the way it should.

I'd like to know what's wrong with it. I've been assured the timing was setup correctly and the transmission has been serviced.