The subject of bearings is vast and your post is a little vague.
Most automotive engines use journal bearings. That is the bearing element itself is an elastohydrodynamic (EHD) oil film. The EHD oil film is generated by the presence of a fluid (oil,) trapped between two close proximity moving surfaces.
EHD oil films are characterized by their film thickness, which is only a few microns. A well designed journal bearing can have mechanical losses close to rolling element bearings, with the benefits of less cost, fewer parts and lower weight.
EHD oil film pressures can be very high (>50,000 psi), and that is why a very small journal bearing area can support huge loads without metal-to-metal contact. Since there is no metal-to-metal contact in a properly designed journal bearing (except during stopping and starting), low friction coatings (like DLC) have no benefit. The only mechanical losses are incurred through the shearing of the oil film itself, and are quite small. Of course, you may also wish to include the losses that are produced by the oil pump feeding the bearings. The flow rate of the pump is based on the amount of oil flow necessary to keep the temperature of the journal bearing materials within their design limits. And these pumping losses are usually greater than the oil film shear losses in the bearing itself.
The only coatings used with journal bearings are soft metal overlays (tin or lead) to provide a small measure of embedability, should the oil become contaminated with hard particles.
As for transmissions, they typically use rolling element bearings (ie. ball or roller bearings). As with journal bearings, a well designed rolling element bearing operates with the rolling elements supported by an EHD oil film. The effectiveness of this EHD operating regime is characterized by the bearing's lamda number. The life of rolling element bearings is defined by the number and magnitude of the contact (Hertz) stress cycles each section of the bearing races see. The efficiency of a rolling element bearing is usually very high, but can be adversely affected by roller/ball skidding, oil churning or race misalignment. Since a properly designed rolling element bearing operates with EHD contact, hard coatings (like DLC) provide no benefit.
The only instance I can think of where a low Mu coating, like DLC's, titanium nitride, MoS2 or TFE would be beneficial, is where you are operating in a boundary lubrication regime. But I don't know why someone would intentionally design for that condition. You would need to limit the contact pressures, the friction loss would be high, and the amount of power being transmitted through the joint would have to be small, or the interface would rapidly overheat and fail.
You said: "I am looking a lowering friction at start up, extending life, retaining lubrication and improving hydrodynamic performance."
With a journal bearing, you do not want to retain lubricant. The most important function of the lubricant is to provide cooling for the bearing materials. You want to design and manufacture the journal and bearing clearance such that you have have just enough oil flow leaking out of the bearing to provide adequate cooling under all operating conditions.
You can maximize journal bearing life by keeping the oil clean and at the correct temperature. And also by selecting bearing/journal materials that have adequate compressive fatigue life with regards to the peak oil film pressures they will see. Journal bearing failure modes are scoring (oil contamination), fatigue (spalling due to compressive/subsurface shear stresses), overheating (inadequate oil flow), or corrosion (oil contamination).
As for improving hydrodynamic performance, keep the diameter of the journal as small as possible while still achieving adequate bending stiffness. The L/D ratio of the bearing should be .30 or greater, as a rule of thumb. I would also highly recommend a journal orbit analysis to determine the optimum location for the oil feed hole.
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