over heating at idle

ok i got an 87 xj with a 4.7 stroker in it still using the stock closed system accept with an aluminum tank instead of the plastic one. now here is my problem i all of a sudden started over heating at idle but not when driving. already replaced the fan clutch and thermostat if anyone has any ideas let me know asap?

Is the electric fan coming on?

Waterpump could be getting weak.

What is the history of routine cooling system maintenance?

Check the radiator for fin rot. You'll never get adequate cooling at idle or crawl speed if the fins have started to fall apart.

Overheating at low speed/idle

1. Fan clutch not engaging--is it engaging, new or not?

2. Water pump not moving enough coolant at low RPMs--replace WP.

3. Insufficient air flow through the radiator--see No. 1 above + rotted/blocked fins, too much crap mounted in front of radiator--a/c, trans cooler, ps cooler, winch.

4. Clogged radiator restricting flow of coolant--flush or replace.