Lately I've been noticing whenever its damp outside or raining my 2004 blazer basically loses all its 'pep' when accelerating, pretty well have to put the pedal to the floor to get to speed up and the tach will go up sometimes to 5k rpm.

All fluids are normal and oil was recently changed, the engine only has less than 90,000 kms on it.

Also when applying the brake or coming to an stop, the oil pressure will drop almost to 0, and will go above normal again once the gas is pressed and truck is moving again. It drops very little (not below half) when dry outside (which I was told is normal)

What could be the problems? Sending unit or plugs or something else electrical?

Any help would be appreciated!

 

Does the engine sound like it's going to 5k, as well?Time for a tuneup, sounds like. Use AC Delco parts only. Do you have a SES lite on?
Is it jerky at all or just sorta 'blah'?
Note that bad ignition modules manifest all sorts of ways..
https://blazerforum.com/forum/engine...-module-68883/

Dont know about your oil pressure, though. Separate issue unless spark is jumping from plug wire to sender wires but that's pretty much a stretch of probablility