95 gxe auto 197,217mi. I replaced spark plugs,crankshaft pulley at 185-190,000miles. At 195-196 my water pump gaskets finally went out after 5-6months of leaking slow. I went to a shade tree mechanic nd he replaced water pump,timing chain,I also had timing cover leak nd acted like I didn't kno so he replaced that also all for 300$ Bcuz he didn't realize how much work it was til after we agreed on price lol. I got car back it rides smooth but it idles lower. Normal idle is 750 meanwhile now it's 500-650. I used to be able to jump str8 to 40no problem but now it kinda struggles. What would be the reason? I also have new muffler on could back pressure of it be slowing me down?