engine hesitates on slight incline unless I floor it, on 1998 Chevrolet Lumina

I feel the engine hesitate on slight inclines when I accelerate unless I floor it. Just recently started. Doesn't seem to make a difference how fast I am already going. At first it only happened at low speed but now also at higher speed.

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1 answer 1 comment
Yes, the 'service engine soon' light is on because we disconected the temp. sensor until I can aford to replace it. The fans were not cycling on unless a/c was on and engine temp guage was reading hot. so now the fans are on all the time as soon as I start the car. UPDATE: replaced fan motors and intake manifold gasket. The gas cap is the first thing I check now when the "service engine soon" light comes on because this seems to be a frequent cause. The car is still overheating.