Timing belt changed, still issues

The only way to get a real answer is to have a mechanic look over the motor. If you don't trust the mechanic you have now, take it someplace else.

Subaru head gaskets leak and you have an older car that is especially susceptible to leaking head gaskets. I think you are unfortunate to have this happen after spending all that money but this is "normal" for Subaru's.

Common SOHC 2.2i or an LS/GT/OB with the fragile DOHC 2.5? The former famously leaks oil at the front cam and crank seals, so those MUST be replaced when "belting" the 2.2; it was called "doing the front package" back in the day. The fancier 2.5 tended to not leak oil as badly, but is an interference motor, often bending a valve if a t-belt snaps. If you've coolant leaking, is it under your "new" waterpump or at a head gasket seam? If oil, is it under the FRONT of the motor (those seals) or the rear (maybe the rear main seal)? Ken is correct in that there are too many potential sources of problems and errors here, such that a solid investigation is warranted. Running for 10-15 minutes then experiencing a loss of power is indeed puzzling. I wonder if the t-belt was installed one tooth off? It won't throw a CEL but will have lost power. You may have to start over here...good luck.