I have a 99 suburban with a 5.7 vortex with an [COLOR=blue !important][COLOR=blue !important]auto[/COLOR][/COLOR] tranny. When I am driving and let off the gas the rpms stay at around 1200-1500 even if I am coasting in N. When I let off the gas to slow down it wont. When I come to a complete stop they will drop. If I am stopped and in park and rev the [COLOR=blue !important][COLOR=blue !important]engine[/COLOR][/COLOR] it comes down to a normal idle. This just started a few days ago. any idea what it could be??