A couple of weeks ago I picked up a 1985 full size blazer with a 305 & a 700r4. I think I am having multiple problems, but I am not sure. When I accelerate from a stop it shifts into 2nd fine. It stays in 2nd gear too long I think. it revvs high, and I am no longer accelerating, and then it finally shifts. The 3rd-4th shift is fine. The hitch is when it is revving high in 2nd gear and I am not going anywhere it has a bad misfire or backfire, or something. Also when I floor it from a start it does ok, but when I am cruzing along and floor it (so that it will downshift into 2nd) it just cuts out & boggs down. Could a simple plug & wire change solve this, or any other suggestions appreciated.  

Sounds like the kickdown cable for the trans needs to be adjusted to solve the holding 2nd gear too long.

On the misfire/backfire issue, I'd do a full tuneup on the motor and see if that solves the problem. The other possible culprit is a worn out valvespring. You mentioned that "revving high in 2nd gear and I'm not going anywhere it has a bad misfire/backfire", this sounds like a case of spring surge to me. Factory valvesprings form that year (and with that much mileage on them) can't take high revs very well.