1998 Buick Park Ave Trans problem

Installed another 4T65E Transmission into this Park Ave. Started up, ran through all gears and when in drive it makes a loud grinding noise. Car will not move in any gear. Could the trans fluid be low? I seem to have a problem checking.

Problem checking fluid?, explain this.

When the trans is cold the fluid is up to the full mark on the dip stick. When hot I am having a problem due to the excess on the edges of the dip stick.