Shift and acceleration problems

I was driving home from work today and when I started going down the road, my blazer was not accelerating like normal, so I pressed the gas fairly hard and it just reved up the engine instead of going faster. The blazer was in drive, but it sounded like it was in neutral. I couldn't tell if it was a shift problem or what. I had to accelerate real slow for it to eventually get up to around 40 mph. Does anyone know my problem?
I dont know if this has anything to do with it but I just replaced my plug wires two days ago, and a couple weeks ago my blown intake gasket was replaced.

By the way, I only replaced my spark plug wires two days ago beacuse I did a complete tune up a few weeks ago and I just got around to the wires. I did not mix up the wires, I did them one at a time. When I did my tune up a few weeks ago I put in a new distributor cap, rotor, plugs, fuel pump, radiator cap, and pcv valve. Thanks for any help, I rely on my blazer.

i got on to ask the same thing, it happened today, it appears to stay stuck in 3rd gear, reverse works. it just wont up shift or down shift, seems to be an electrical problem, needle jumps from 0-40-60 its all mest up, its 27degrees, amd i might have to ride my motorcycle to work tomorrow if this keeps up
please advice

i really need someone to tell me what could it be

Shift manually from 1st up as you accelerate. See if you get gears. These two problems could be different from one poster to another. Either way check your fluid level, and make sure its at the proper level. Also, jorgeandonie, get yours on a scanner and see what it is showing. If the speedo is jumping up and down, you need to check and make sure the computer is getting proper readings from the VSS(vehicle speed sensor) The computer needs this to make the transmission work properly.

How long has it been sence a trans. flush on your blazer?

ignition switch? i was having the same problem in my 97 one day headin into the city, took it to a tranny shop, and for free he scanned it and told me it was the ignition switch, since its replacement problem never came back. what year is the blazer? not sure if u posted it or not, didnt see it up there.