2001 Ford Focus 01 Ford Focus screeches when I try to start

Recently I've had some work done on my 01 Ford Focus. About a month ago I had a PVC hose replaced due to it being collapsed, and my main air tube was replaced due to rodent damage (also check engine code came up "Too Lean", and has since gone off). About 4 days ago I had a new battery installed by a shop. This same shop notified me that one of my valves was leaking a little oil, but no word on it being collapsed or anything of the sort. I was due to be in another city, so I took off that day and drove about 70 miles, then about another 80 the next day. Today my car stalled 3 times.

The first time it stalled I was driving uphill, and there was some smoke. I put the car in park, waited, and restarted it without much of a problem, then drove it up a steep driveway - it jerked and seemed like it make lose power, but made it all the way up. The second time was at a stop light on a flat road surface. The power cut off, I was able to roll it into a parking lot and restart it. I left it parked for about another hour, then idled it for about 10 minutes before driving it to a gas station to fill it.

After driving about 12 miles I was back home. I stopped once along the way but the car started no problem then. When I was coming up the same hill as before, the car started to shake and felt like it was losing some power. I shut it off, waited a few minutes, then tried to start it. LOUD screeching noise. I tried again and the same thing happened. When I tried a third time it started and once again I got it up the steep driveway.

Since getting back to the house, I've checked the oil (full) and the transmission fluid (full). I have to drive 150 miles tomorrow and desperately need my car to make it. Tomorrow is also a Sunday, which makes getting it into a shop all the more difficult. I thought if the oil had leaked it would be dry, but there's plenty of oil in the pan. Somebody PLEASE HELP. Again, brand new battery, possibly a small leak in one of the valves, but this is a totally new problem since having my battery replaced!