AW4 noise

Got a used 1996 Jeep AW4 from auto wrecker and they claimed it got low mileage and had been sitting on the shelf for 11 years . Just installed it today and everything work except that when going from D to P there is a loud brake squeaking noise inside the tranny for about 5 seconds then no more noise . Same thing if going from P to R and shift back to P will be another loud noise for 5 seconds , but the strange thing is if you put it in neutral and wait 3 seconds then directly shift to P without stopping at R then no noise ?? Did find some rust inside the transmission pan when they drain out the transmission fluid long time ago . Also not too sure if there are rust inside the transmission and causing the valves sticking ?

Anyone have any insights or what the problem may be ?

Thanks in advance

Probably a lot of buildup and hardened seals. My junkyard trans shifted dirty for a while too. Small bottle of CRC Trans-X available at your neighborhood vatozone will clean the metal and swell the seals. Drain and refill the trans fluid after 500-1000 miles.