2001 Suburban transmission

Bought this vehicle recently with 92,000 highway miles, no towing. Everything seems fine, but no major service has ever been done other than some A/C work, brakes and oil changes. Last night I was trying to back out of a parking spot and slipped it into reverse. The truck rolled forward in neutral! Tried twice and then thought I maybe didn't have the brake pedal down, so tried again and it was OK. This has not recurred.

Is this a known problem and a warning of further trouble? I plan to have the transmission fluid changed, but should I have the mechanic check for anthing else, like cable problems?

Thanks...