95 4.0L Tach Issue

I have been through quite a few threads and couldn't find anything like this. I just swapped my 2.5L for a 4.0L. I finally got it to start and have run into a couple issues. First, my tach reads 800 when I start and only goes to about 1100 when I am driving it. I was in 15 mph in low and still only read 1100. Second, my autotrans isn't shifting quite right. Without having the tach reading correctly, it is hard to tell when it is actually shifting. Any troubleshooting hints on the tach issue would be appreciated.