I have a 89 chevy k1500 that I recently had a oil sending unit installed on because old one was leaking. Now the oil presure auge keeps bouncing back and forth. It doesn't normally get any lower than 30 but will occaisionally peg all the way to right. It is normally under aload when it does this and at the same time the temp. will increase up above 210. What do you think could be causing this?