Olds 94 98 fuel milage/ ignition problems

I have a 94 olds 98 with a v6 not supercharged with approx. 135k miles. I bought it about 26 mths ago with about 190k miles on it. It was getting 19 miles to the gallon and cranked right up first time ever time.

About 9 months ago i noticed my mpg started to drop.When it got around 16 mpg after 4 months of this the car would stall out at 1/8 of a tank when i had previously had been able to run a good 50 miles after it the empity line ( i tried not to do this very often). Now i have to fill it up at the 1/4 tank mark. I average 150 miles between fill ups now when i use to get 325 plus. I did change the fuel filter and pump about 1 year ago so i doubt that they are the problem.I have changed the oil ever 3500 miles or less and rotated the tires a few times with new tires a year ago. I have considered replacing the egr valve and the o2 sensors but they are a little pricey for me at the moment.

The ignititon problem started 2 mths ago. Just 1 day out of the blue it had a hard time cranking first thing in the morning, summer time so it wasent cold out , and every time i went to restart the car it took several attempts to get it started.

Thanks for any help and advice yall can throw my way.