i just had a new muffler put on my 2001 blazer and now the car stumbles at high rpm.it has no power.someone told me to undo the battery than hook it back up so the computer in the car can re calibrate?thid true?

Yes and no on the computer thing. Worth a try. It is possible to install a muffler backwards, not sure of the effects of this but may be worth finding out. What brand/ size in and out is your muffler. and did you put if on or a shop?

why did you have to replace the muffler? Do you have a check engine light on?

The only reason a muffler would have to be replaced would be because it rusted out, it wont cause a check engine light but you can fail a safety inspection for it.

It is common for converters to come apart internally. I have done quite a few on these vehicles. Sometimes when they come apart they plug the muffler causing backpressure issues. Thats the only reason i ask. extra flow with new muffler could case internals of convertor to move more and cause intermittent driveabilty problems.