Pull the MAF sensor out, and if its not a pretty shiny end, take some brake cleaner (brake, carb, b12, etc... SPRAY cleaner) and spray it clean, then let it dry and put it back and see if it makes a difference, DO NOT touch it with anything, its a fine tuned sensor and with age can be brittle and break if you touch it, it wont break under normal conditions just spray it clean vs using a q-tip and alcohol...
most likely a tranny issue, a 40mph lag or shutter occurs in some from what ive seen... not sure on a solid fix tho