GMC 1999 Jimmy 4.3L V6: DTC P1902 Meaning and Symptoms Explained

I own a 1999 GMC Jimmy with 4WD, SLE trim, 4.3L V6 engine, currently at 140,000 km. I'm experiencing several driving issues that have started to concern me. SYMPTOMS: - Engine warning light comes on steadily while driving - Anti-lock brake (ABS) warning light activates during operation - On hills, the vehicle lacks power and hesitates when accelerating - During acceleration, the engine stutters and occasionally jerks - Backfiring is observed through the exhaust pipe while driving - From a stop, initial movement is sluggish before it improves - During at least one gear shift, the engine races before engaging the gear - Tachometer needle bounces erratically during operation - In wet weather, the engine light flashes yellow and then stabilizes after deceleration; it turns off when roads dry up I recently had a maintenance service including: spark plugs and wires replaced (cap and rotor not changed), fuel filter replacement, water pump replacement, coolant flush, idler arm, tie rod, and front wheel bearings. CODES RECORDED AT LOCAL SHOP: - P1902: Transmission-related fault code (GM-specific) - P03003: Cylinder misfire detected - C0225: Left front speed sensor issue - C0226: Right front speed sensor issue - C0227: Left front wheel speed sensor erratic reading - C0-225 and C0226: Left front speed sensor open circuit WHAT IS WRONG WITH MY CAR? I understand that P19xx codes are specific to GM transmission systems. So, what does P1902 actually mean in this context? How can I diagnose or fix it given the symptoms and other related codes?