2000 Yukon Denali 5

2000 Yukon Denali 5.7 litre 110k miles. The engine rpm stays high after lifting foot from gas pedal while stopping from speed or just slowing. If you place transmission in neutral while rolling, the tach will settle at around 1800 rpm as long as the vehicle speed is above 5 mph, then will drop quickly to 800 rpm when slowed below 5 mph. The rpm will not increase if transmission is placed in gear while stopped.

Had intake gasket replaced recently and have some instruments reading "low" even when operation is normal.

H E L P! It's dangerous.