Trying to beat the heat here in Phoenix, I started to track trans temps on my '01 4x4 Expedition with 5.4 and 4r100. Trans temps were routinely above 200f driving around town with OEM trans cooler (towing pkg). Hit 220f and higher driving slow speed off-road up steep hills in D. Such high temps were alarming so I decided to try to get it under control. Modified my driving habits and that helped considerably, and decided to add a trans cooler. Added a Hayden 679 cooler after the aux cooler and that helped, dropping temps about 20 degrees average. On the freeway trans temp was stable around 190f, and every now and then went above 200f on steep hills off road in D. Considered adding a 33 row cooler from 2000's F350 6.0 turbodiesel, but decided it wouldn't fit without a lot of modification. A 25 row cooler would fit, they're cheap at used auto parts but it's hard finding one in good condition. Since I already had one Hayden 679 I decided to add another. This dropped trans temps 30-40f which I consider satisfactory. Ambient temps have been above 110f for the last 30 days here and the trans rarely goes above 170f and maxed out at 192f on a long steep hill that formerly would push temps up to 220f. The trans coolers are mounted horizontal with tee fittings at the inlet (lower fittings) and outlet (upper fittings). I used two 1/2 x 3/16 x 36" steel straps to mount the coolers. They're bolted to the front of the radiator support, to existing bolts that happen to be the right distance apart to span the oil cooler mounting holes. I put foam insulation tape between the coolers and steel bars to reduce chafing the coolers. The steel bars bolt between the grill support brackets and radiator support. Only needed to drill holes in the steel bars, not the vehicle. Only vehicle parts that needed to be modified were cutting the transmission lines to the aux trans cooler, and the ambient temperature sensor bracket, had to bend it straight and angled downwards to clear the cooler fins and leave clearance for the big plastic cover over the condenser and radiator. Foam tape hopefully will reduce chafing for the cooler plates against the steel bar. The cooler fittings are facing each other, connected with tee fitting. The lower is inlet from aux cooler, upper is outlet, goes to transmission. Covered the hose with plastic wire loom to hopefully protect against chafing. The aux cooler was retained, the rubber strain relief on the OEM transmission lines were cut and spliced to the coolers with 3/8" connectors.