1995 geo tracker

My car starts up easily in the am. But if I drive it 5 miles or more and ki it to go in the store and start it back up it spins over and over and eventually it will start. Also it idles real rough is coughs and sputters it only has 116,000 mi on it. I filled up the gas tank the other day ($25) and it only went 113 mi til empty. Sometimes it won’t idle enuf to keep it run ing and sometimes, like today at the drive thru it idled up so high I thought it would just take off. I have replaced the fuel pump, battery, all the fluids, check engine life comes on and off. Mostly on. now my mechanic Wants to put on a new computer and a sensor? Help! I only paid $750 for the car but have spent almost that much on repairs. Please help. I was married to mechanic for 24 years but he had kids with his exwife during our marriage so I can’t take my car to him for advice….lol.