With Insulin resistance, that means your body isn't utilizing insulin as well as it should. With that, your sugar goes up. Your body tries to compensate by pushing out even more insulin to counteract the high sugar.
"Two hour after most meals I run about 160 to 250"
Your doctor is telling you that you are prediabetic with numbers like these?
Might want to request an OGTT (Oral Glucose Tolerance Time) from your doctor. It's what is used to diagnose - but a couple fasting sugars above 127 (or 128?) is used also. How are your fasting sugars (blood sugar taken after 8-12 hours of no food)?
With your sugars like that, he hasn't ordered a Hemoglobin A1c (aka A1c, HbA1c, HbA1c)?
I'm not a doctor, but yes, those numbers seem high. You are not in any immediate danger or anything like that, but you are going to want to get to the doc and figure everything out. Your doctor should steer you down some pathway. If he doesn't and wants to keep playing things by ear, you should probably find a new doctor.
I'm not trying to be mean, but the odds of high insulin and sugars in that range being something OTHER than diabetes have to be extremely low.