I have a 1996 blazer that wont down shift any ideas?

Your blazer is on a safe mode and need to be brought in to a transmission shop before you burn out the 3rd gear. They can scan the blazer to see if it's a wire harness problem or the B solenoid has failed and needs to be replaced. The solenoid cost around $25.00, but it's in the back of the valve body. It takes about 5 min to replace, but you have to drop the transmission pan so you might as well get the transmission service also. The other common failure is the wire harness from the ECM to the transmission has failed and needs to be replaced or repaired. The harness is around $125.00 at the dealer, and the last thing that has gone bad is the Ignition switch it self and needs to be replaced. Start with checking the transmission fuse in the fuse box by the dash on the drivers side, if the fuse is good try this. Turn the ignition keys to the run position "engine not running" and pull the ECM (BATT) fuse out for 20 seconds. Place it back in and start the blazer, it may stall but let it, just start it again and then go for a test drive. This will reset the ECM and will reset the transmission module also, if problem still there then a transmission shop can hook up a scanner and determine if it's going to be weiring or mechanical. Good luck and keep me posted.