1994 Honda Passport Lack of power going up hills

I recently had some hoses, thermostat and fan clutch replaced. The radiator is 2 yrs old. Original problem was thermostat was sticking. As soon as I got the car back I noticed I had lost power going from a stop, then shortly found out going up hill where normally I could go 5th gear 65-70. I had to downshift to 3rd just to stay at 60. I took it back and they tell me nothing is wrong. Im the only owner of the car and it 180 difference power wise than when I dropped it off. Any ideas of what might be going in? Also, check engine light goes on/off from time to time. But according to this shop nothing is wrong. I'll take it somewhere else, but maybe some insight as to what the cause might be would ve helpful. Thanks