here are some TSB's you can check out that may be related, namely the first one.
99-18-05
PERCEIVED 2-3 DELAYED UPSHIFT, PRIMARILY WHEN THE TRANSMISSION IS COLD, POSSIBLE DTC P0782 PRESENT. - TRANS CONTROL INDICATOR LAMP (TCIL) LIT WITH (DTC) P0782 STORED IN MEMORY - VEHICLES BUILT BETWEEN 3/15/97 & 12/31/98 AND WITH 4R70W
TRANSMISSION
97-12-13
TRANSMISSION - C6, E40D, AOD, 4R70W - LOW TRANSMISSION FLUID LEVEL AND/OR SHIFT AND/OR ENGAGEMENT CONCERNS - 4X4 AND AWD VEHICLES ONLY
97-11-11
TRANSMISSION - 4R70W - ERRATIC OR PROLONGED 1-2 SHIFT TSB REPLACES OASIS SSM # 10002
02-13-08
TRANSMISSION - 4R44E/4R55E/5R44E/5R55E - LOW LINE PRESSURE READING AT WIDE OPEN THROTTLE (WOT) - SLIPPING SHIFTS AND/OR DELAYED ENGAGEMENTS - POSSIBLE DIAGNOSTIC TROUBLE CODES P0732, P0733, P1762 SET - VEHICLES BUILT BEFORE 12/01/2001:
REFER TO THE TSB SERVICE PROCEDURE FOR DETAILS.