RPM Trouble

[Ak_Titan]

I have a 93 240 conv. A little history......
I bought the car about three years ago and it is pretty much stock. When I first got the car I had to put new fuel injectors in it and gave it a really good tune up. I had it sit sitting at my aunts place for about a year in an enclosed building because I moved to alaska. I drove the car up in a trailor and have hardly drove it since.
Just recently I have been driving it around and it starts and runs good but when I accelorate to fast the rpm's drop out and the car shuts down. then when I go to start it back up it, it almost acts as if were flooded. but when I let it sit for about 5 mins it fires right back up and drives fine. I also noticed too that when I'm in park the rpm's drop from 900 to about 500 and it acts like it is going to stall out.
Could some one please help cause I have brought the car to 3 different places and no one can tell me what it is.