I have a 2004 Chevy impala LS 3800 series 2 160k. I changed radiator. When I started the car I heard a swirling whooshing sound of fluids I thought initially were going to my heater core however now I have p1811 code and hard shifting when the car warms up. I thought I might have lost too much fluid and added checked while hot and in park on flat ground and it was in the lower end so I added Lucas stop slip. It seems ok in the begging but still is slipping and getting long hard shifts. I know the common issues are TPCS solenoids. I’m wondering what would be a smart decision I don’t have tons of $$ and I got the car cheap. Engine is running great!