Sounds like the distributor may have moved a little and the timing is retarded. Check timing and re-tighten bolt to hold distributor clamp down a little tighter. Also your spark plug gap measurements are in mm and most folks on her use inch measurements as in .035 or .045 in. Try gapping the plugs to .045 = 45 thousandths With EFi and a good coil you can usually gap even a little larger. Newer cars use gaps of .060.
1) Checka and re-set timing
2) re-gap plugs to .045
Drive car and recheck plugs after 20 miles or so. Good luck