i would say your tach is fine....sure you went up to lets say 10,000 rpms. no...your tach doesnt max at 8,000....sure...the writing on the tach says eight...but in reality you can go all the way back to zero (because there is a bump stop do-dad there). like i stated earklier....STOP RELYING ON YOUR TACH!!!!!!!!!! pay attention and listen to what the car is doing and feeling...stop worrying about your gauges...they are there for reference only and really have no meaning once you find out in the beginning of tuning the car.......

for example....your gas gauge....you only need it in the beginning of buying or driving the vehicle. do you satre at the gas gauge??? no....you glance at it. from then you can realize how long you can travel or whatnot. from that beginning glance you can actually trip the odo and then never have to worry about your gas gauge again...just fill it up at 200 miles.

another example...boost gauage......you only need it in the beginning of the tuning process.....from then on out...you are not staring at your boost gauge. only there for reference. trust me....if the wastegate fails....you will feel a surge of power or vice versa.

now the final example...the tach....once you get good enough...you can hear where the car is at rpm wise. i dont even look at my tach anymore when i am racing...

so to close things up here....pay attention to what the car is doing??? does it sound like it is at 5,000 at 70? or does it sound like it is at 4,000 at 70. sure...put a new tach in it...but you are just wasting money....it is in wiring not the gauge itself.