1997 Subaru Legacy

My 97 subaru had bad head gaskets but run fine but got hot replaced gaskets had the heads and valves done all is good. Put togather and has cly. 2&4 missfire plugs wires has been replaced twice not the prblem the timeing belt has been replaced twice in time. No intake leaks at all but pluged off the brake booster and the miss is better but still there. Before the head gaskets run fine.
HELP!