2000 Chevy Venture transmission delay

Several minutes of delayed engagement is extreme, it could mean internal seal leakage. If you have this accompanied with noise, it is probably on it's way out, it is just a matter of time before it don't move at all. What does the fluid level, and condition(color, odor) look like. If it is accelerated to noise, and operational symptoms, more than likely a fluid and filter service won't be enough.