93 sable 3.8 engine prob after new radiator

my 93 3.8 sable ran fine. radiator started leaking. had local shop, used by family, do r/r. mechanic also replaced stock 195 thermostat with 180 degree.
took the car 5 miles to a drive-thru atm. battery light came on/off, car had poor power---auto-tranny was awful---then it died---had it towed back to shop. mechanic denies any responsibility---i usually hear fan come on, never did. suspect fan sensor damage, or something. while waiting to pay and leave, a NAPA 'parts-runner' delivered some parts for another car and the shop owner 'went-bonkers', insisting the parts were wrong. the NAPA guy had him go over his order. he saw it was correct. i hate litigation, but how do you deal with either 'demented' mechcanics? or unscrupulous ones? any ideas what led to this? thanks.

Get a second opinion from another shop.

thank you for your attention---but rather than trust 'another shop', i think it best to rely on former sable owners on this forum. i'm very interested in Why the stock 195 thermo was replaced w/180---i suspect this 'threw-off' the computer, hence poor tranny performance, fan not actuating, etc. meanwhile, i'll look for an pre-'75 toyota, peugeot, volvo---those i need no assistance with. thanks again---best regards--