My 97 XLT has a sporradic problem with shifting into reverse from park. Sometimes I will shift the car into reverse, the RPMs drop slightly, but the car will not move. If the engine is revved to about 1500 RPM, a loud bang can be heard from under the car and the reverse gear engages. Also, and it seems to be related, sometimes when I park the car I have to get out and push the car forward to get it to engage in Park. Any thoughts? The car as 134,500 miles on it with the original 55R5E transmission and BW 4405 T-case.