1998 Chevy Blazer Leaks fluid out of the bellhosing, but, only at high RPM's?

Make sure you have power to the fuel pump. On this model you should hear a quiet high pitched mosquito in your ear sound when you have all the lights on the dash panel just before you turnover the engine. If push comes to shove, take the fuel pump out, keep the power on it and run it through a bucket to see if you can at least pump water through it. Make sure you let it dry out all the way though before placing back in the tank.

transmission slipping could be low transmission fluid level or need a transmission fluid and filter change.if transmission fluid was real low check for transmission fluid leaks around transmission oil pan gasket or fluid leaks around cooler lines or torque converter shaft seal. if you getting steam inside cab.your heater core is leaking.if transmission fluid level okay and filter been changed could have faulty over drive switch.

If the fluid is full and there are no external leaks, and it is still malfunctioning, I would try to flush and refill the transmission with new fluid to see if this rectifies the problem. If it doesn't, then there is a problem with a shift solenoid where the transmission will have to be reserviced and perhaps torn down and rebuilt again (I know this is dreadful). Try to see if there are any codes stored on the computer for the transmission that might point to a clue about the problem you are experiencing with it.

Try giving it a shot of starting fluid. You don't say if it's actually firing. If it tries or runs for a few seconds off of the starting fluid then try changing the fuel pump relay. It's inside of the glove box on the left hand side behind the little door. If that doesn't work it's most likely the fuel pump.

The 4 speed auto. has a check plug under the car start the car remove the plug if fluid pours out your good if it doesn't pour fluid in untill it starts to pour out and then re insert the plug. (fluid goes in the top of the tranny through the fill hole) hope this helps.

There's a red handled dip stick located on the rear of passenger's side of the engine, this is the place you put in the fluid and check the level. A small long necked funnel helps, be carful not to overfill it as doing so may cause a major leak from over pressurization.

A fluid leak that is pink and/or red colored is usually either power steering fluid or transmission fluid. I recommend checking both. You can check the power steering fluid when the car is off. However, the transmission fluid should be checked with the engine warm and idling in neutral. Have someone else step on the brake or use the parking brake and block the wheels while you're measuring the transmission fluid level.

Your going to have to get the ECM scanned, Auto Zone scan's for free and most garage now will scan for $10.00 to $15.00 since they all have the scanners now and need the business.
You could have a Vehicle Velocity Sensor (V V S)  going bad or the wire harness it self. The V.V.S tells the ECM how fast the drive shaft is rotating and calculate's what gear it should be in relative with the engine speed and throttle position, and transmission fluid pressure.
Regardless you need the Blazer scanned to pin point why your transmission is shifting the way it is. Could be as simple as time for transmission oil and filter change for $125.00 or a loose wire harness.
Check your transmission fluid and try not to run the blazer to hard, to replace the transmission start at $1,900.00 for a rebuilt.
Good luck and hope this helps. Keep me posted

Sounds like the transmission needs a rebuild.