Tach installed and I have ?'s

[PHOENIX]

I never had a tach before in my truck. I installed this one (http://www.jegs.com/photos/1054495.jpg) this weekend. Anyway I followed instructions 100%. I think its right but im not sure. I still need to figure out what rear end I have (i know that would help alot). But I have a stock 350 w/ sm465 tranny. (2wd). The engine seems to be racing alot, but the tach only reads 3k. Is that normal? Does your truck sound like its racing alot at 3k? I did some freeway driving and heres what I got:

70 mph = 3,000 rpm's
75 mph = 3,500 rpm's
80 mph = 4,000 rpm's

Thats not cool at all! No wonder my truck gets hot when driving at higher speeds. I need a new tranny and rear end! Im gonna find out what rear end I have and post it.

Anyway my truck is racing alot at 3k + I would be afraid to take it anywhere near 4800. Give me some feedback. What do you guys think? The tach matches my timing gun at idle as far as rpms. I cant see the timing gun when in the truck so I need to get someone to hold it and watch it as I test it. Im sure its accurate, but Ill test it anyways.

Just looking for some feedback with your expierences.