Why do I have no passing gear acceleration in 96 XJ6?

What is your question?

96 XJ6 with check engine light (was blinking, but not now) will not accelerate, but rather bogs down when attempting to use passing gear. Gears seem to shift once pressure is reduced on accelerator. Gets up to speed steadily with constant, gradual pressure on the accelerator. In the past it ran sluggish on inclines, but that was not the case this last time I drove it approximately 20 miles in 55 mile zone. (Achieved and maintained 75 mph with no problem). Cruise control works, but I did not test it for uphill acceleration.

What makes this problem better or worse?

Unsure

How long has your 1996 Jaguar XJ6 had this problem?

2 - 3 Months but car is not driven daily. Perhaps 3 times in 3 months