Engine stalls going up steep incline

Hello I have a 1987 NISSAN PULSAR NX SE with 110,000 miles. It is the 16Valve DOHC engine. This car sat for 5 years. It runs like a top on level and downhill inclines but uphill it loses power, stutters and tries to stall. I'm sure there is plenty of old gas in the tank and I'm thinking fuel filter may be clogging with debris. This is my first Japanese car and for cheap but would like to get it running reliably. Your suggestions are appreciated.

Mark