my nissan 1997 altima gx seems to have a high rpms (3000-3300rpm) when going 70mph is this normal? If not who repairs transmission or mechanic?

That's not too far off depending on gear ratios and number of speeds. In older days, with a final drive of 1:1, you would run a 1/2 ratio 3500 @70. However my 2006 Nissan Frontier runs a 6 speed and is 2100 @ 70. Worth a visit to a transmission shop to check.