Power Loss & Leakdown test

87 with a 2.5 L4. Little over 3 years ago I bought a rebuilt long block, its been down on power this last month. Finally got around to some tests, was going to check compression first but only had leak down tester at my shop. Going to have to find my compression tester.

Middle two cyl are marginal at best. Engine starts, idles & pulls fine other than low power evident on hills @ freeway speeds. No smoke or popping on intake or exhaust sides. Oil & coolant are both clean. Anyone ever see head gasket fail between middle cyls? Going to borrow a bore scope from a friend this week & see if anything else is evident before tearing into it as this is a daily driver.

btw - header, larger exhaust, weber on the stock intake.

TIA.

My head gaskit blew there an i lost a lot of power. Dos your radator cap have a lot of brown rust looking shit on it? Are all your plugs look somewhat the same? Do u ever run it really low on fuel before u fill it up? All your plug wires hooked up?