have an 06 megacab, previous owner always took it to the dealer for oil changes. Decided I'd make to switch to a synthetic so went ahead and went with rp 5w20 and everything was good for the first bit, but now the oil pressure drops frequently. oil level is up, no leaks at all, so not sure what the issue is here

 

Unless its an MDS engine pretty sure you should use 5-30. my 04 requires 5-30.

 

Clean your pick up screen..

 

Chances are you switched all at once, on a engine that had dino oil in it all its life, and the full syn cleaned all the deposits of the internal surfaces all at once, now they're in your oil pan, clogging the oil pickup, as mentioned above. Only remedy is to drain it, pull the pan and clean it out.

You wouldn't be the first person this has happened to, a gradual change over with very short drain cycles, substituting quarts of syn for dino quarts each oil change, so the deposits are gradually desolved

 

It's fairly common when switching to a synthetic that it will carry ALL the sludge that is in the system from conventional oil right to the screen and clog it. The problem is that the synthetic actually works TOO WELL in loosening the crud and it overcomes the screen.

I usually do the first change in an engine with over say 50k in conventional oil use with a blend first so as not to clean all the crud all at once. I've never read any concrete evidence that doing a one time blend to ease into synthetic is beneficial, just something I've always done.

I'm with drew on this - clean the screen...

 

I bought 5w20 once by accident and decided to just go ahead and use it. Saw a slight decrease in pressure, nothing major though. Needle sat at like 11:55 vs 12:05 with the 5w30

 

These trucks call for 5w20. Why would it be a problem? Ive been running this wt Mobil 1 since the trucks first oil change. Still use it at 114,000 miles, no problems. Mine is an 05 if that makes a difference.

 

'03 & '04 called for 5w-30 when they were introduced. The '05 (which is identical to the '04 except PCM/Tranny tuning) called for 5w-20. Even dealers now use the Chrysler recommended 5w-20 in '03s and '04s.

In non-MDS (pre-'06 & 2500/3500) Hemi engines I see no problem using either 5w-20 or 5w-30. MDS is however very specific to 5w-20 oil...

 

Switched to synthetic at 6000 miles and used 5w30. At about 40K went to 5w20 in the winter and never went back. I feel it reduced the tic abit, but the bonus was that I went from being low a quart at the next change to lossing almost none. At 90K still does not use any oil (ok a little on the stick). If the pressure drop is nornally at idle, put a mechanical gauge on it to ensure it is not the sender, connector or gauge.

 

I run RP in my 04 5.7 and still do to this day. Never an issue. My thoughts, replace the oil pressure sensor. Its cheap, easy, quick and several threads on the site with guys having the same issues