Hi, my 84 300td is very sluggish and smokes a lot (kind of white-ish) after a cold start, and then it is ok after the water temp reaches about 80 c. Where should I start looking? thanks

How cold is it in Santa Barbara? It's normal for a diesel, when cold, to be a bit sluggish. Are you just jumping in and taking off? Try letting it idle for a few minutes before taking off, if it cold. Are you getting any nailing or anything else unusual? or it's just slower than usual?

__________________
1983 Euro 240D 277K
2016 Mazda 6
Coming Soon, 2013 Mercedes E350 Bluetec
Formers:
2012- Mazda 3
2007 Outlander- complete pile
1995 E300 Diesel 208K
2007 VW Passat 2.0T 63K SOLD
2003 Jaguar X-type 3.0 Sport Sold 04/11 w/88K
2009 Lexus RX350 9061 miles. Sold 04/09
2008 Mitsubishi Lancer GTS:Totaled Sept.,09 @ 24,000
2003 Infiniti I35 58K Sold
1984 300 turbo diesel 222K

its about 45 to 55 F here. I don't know what nailing is, but it pings a bit. I warm it up for about a min. IT smokes a lot and it has very Little power.

White Smoke can be Coolant or atomized Fuel that did not burn. You might be able tell if it is Fuel by holding a clean Rag near the Exhaust Pipe and smelling the Rag to see if it smells like Fuel.

If the IP Timing is retarded/Late it will cause white smoke; I had this happen to me when I miss installed my Volvo Fuel Injection Pump. Making the timing right fixed it.

To a lesser extent worn Injector Nozzles can also cause it but it is more normal for the smoke to be gray.

Checking the Glow Plugs is easy.
Valve Adjustment may also help.

__________________
84 300D, 82 Volvo 244Gl Diesel

I think it is transmission problem, it doesn't down shift when it is cold its stock in the 3rd or 4th gear when I am going 10mph. I go to neutral and the engine revs up with no hesitation but he auto transmission won't down shift. This only happens for the first 5min after the cold start and its fine after that. Is transmission fluid need to be warmed up before it can work properly, Any ideas what to do? thanks

Almost any problem that indicates fuel supply might be involved. The first thing is to change the fuel filters. Otherwise the problem is never resolved or you just land up going round in circles until you do in many cases.