RRR is bang on the money. Get a 2 row rad with 1.25" tubes. It's a matter of surface area. Bigger tubes allow for more fluid to be cooled while passing through. Most 3 row rads have 0.75” (approx) tubes, which is much less surface area.
Also,have you confirmed that your T-stat is operational? Put the front end on jack stands (this will also allow you to purge out any air in the system which may cause heat pockets), take off the rad cap, start your car, and watch the fluid in the rad for 3-10 minutes. Once it hits the temp your T-stat is designed for (160-185) the coolant should start moving. If starts moving, IMMEDIATELY replace the rad cap. If no movement happens, start with a new T-stat.
