Actually, I-8's highest point is just over 4000 ft. You'd have to go to the top of Mt Laguna (not on I-8) to get to 6000 ft). The climbs are gradual - only one point ("Japatul Hill", we locals call it) is a climb enough to slow trucks and RV's down. It won't bother a car.
GLC - I'd forgotten that the 52 finally opened! I haven't been on it yet. Yes, 52 will definitely get out of San Diego traffic unless you decide to run that between 2 pm and 5 pm. :-)
As far as I-8 goes - - we just drove that into Arizona (Stanfield) last weekend, and there was no construction any more. They were done with the stuff on either side of Gila Bend, going eastbound. (There was a little, westbound, around Yuma. Nothing major, though they wanted to slow us down to 35 on a Sunday when no construction was actually being done. Grrrr!)